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Handout A Gentle Introduction to GIS

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1. Next you will add fields to the attribute table Normally we give field names that are short have no spaces and indicate what type of information is being stored in that field Example field names may be pH RoofColour RoadType and so on As well as choosing a name for each field you need to indicate how the information should be stored in that field i e is ita number a word or a sentence or a date Computer programs usually call information that is made up of words or sentences strings so if you need to store something like a street name or the name of a river you should use string for the field type A Gentle Introduction to GIS 37 4 DATA CAPTURE Figure 34 Creating a new vector layer is as simple as filling in a few details in a form First you choose the geometry type and then you add the attribute fields File Format ESRI Shapefile y Type e Point Line Polygon Attributes Type String ala Type String Notes String The shapefile format allows you to store the numeric field information as either a whole number integer or a decimal number floating point so you need to think before hand whether the numeric data you are going to capture will have decimal places or not The final step as shown in Figure 35 for creating a shapefile is to give it a name and a place on the computer hard disk where it should be created Once again it is a good idea to
2. e Try to identify which symbology types you would use for the following types of vector features points showing pH level of soil samples taken around your school lines showing a road network in a city polygons for houses with an attribute that shows whether it is made of brick wood or other material Something to think about If you don t have a computer available you can use transparency sheets and a 1 50 000 map sheet to experiment with different symbology types For example place a transparency sheet over the map and using different coloured koki pens draw in red all contour lines below 900m or similar and in green all lines above or equal to 900m Can you think of how to reproduce other symbology types using the same technique Further reading Website http en wikipedia org wiki Cartography Map_symbology The QGIS User Guide also has more detailed information on working with attribute data and symbol ogy in QGIS A Gentle Introduction to GIS 32 GIS FOR EDUCATORS Table 8 An example of a table that defines the feature types and the kind of symbology you would use for each Real world feature Geometry Type Symbology Type The school flagpole Point Single Symbol The soccer field Polygon Single Symbol The footpaths in and Polygon Have your learners count the number of learners us around the school ing each footpath in the hour before school and then use graduated symb
3. Further reading Whats next ason oe BB we Ba Vector Attribute Data Overview 00000 eee Attributes in detail Single Symbols 000 Y JO 010 Nn 10 11 12 13 13 13 14 16 16 17 19 20 20 20 GIS FOR EDUCATORS Graduated SDE lt arcar retraga a kaaa SSEELE OSS GO S84 ES 26 Continuous Colour Symbols 2 666 ea ee ee a ek ek ee AA 28 Unique Value Symbols 0 RES EKG ER ae ER ARA ee 30 THINGS io be aware Of osas hk wee Ree EHO ewe ea ES ES Eee ee E 31 What have we learned ee 31 INSI 2263 365 284 Oe A 2 CODER 42 SG BESO 32 Something to think about ce oe ere She Ok Ce hoe be A oe SES Cee we o 32 Further reading s o c 6 ce ca tw Re a a e a id 32 WNA SNET caoat RRA os Ee is sed a G 33 4 Data Capture 34 A III IEEE 34 How does GIS digital data get stored o o e e 34 Planning before you begin lt lt cese io Ee A A 35 Creating an empty shapefile 24444442 da A a A dd a oS 37 Adding data to your shapefile e e 39 Heads up digitising lt lt ici da Aa A 41 Digitising using a digitising table so lt ooc ee ee ee 42 Common problems things to be aware of 2 ee 44 What have we SINS A E a ee ee ROR a aNG 44 PO io w saco See oo eS Bee Ge a a E ee a Ge 45 Something to think GOW 22 24 424 2444466445264 4445446446 LS G48 4 SS ES 45 Furnier reading da oe ek Se Be oe
4. icals that kill plants and animals Using raster data from satellites can help us to monitor for these type of problems Town planners can use raster data from satellites to see where informal settlements are and to help in planning infrastructure Something to think about If you don t have a computer available many of the topics we cover in this tutorial can be reproduced using an overhead and transparency as it uses the same technique of layering information However to properly understand GIS it is always better to learn it using a computer Further reading Book Desktop GIS Mapping the Planet with Open Source Tools Author Gary Sherman ISBN 9781934356067 Website http www gisdevelopment net tutorials tuman006 htm The QGIS User Guide also has more detailed information on working with QGIS What s next In the sections that follow we are going to go into more detail showing you how to use a GIS Appli cation All of the tutorials will be done using QGIS Next up let s look at vectors A Gentle Introduction to GIS 8 GIS FOR EDUCATORS 2 Vector Data Objectives Understanding of vector data mod els as used in GIS Keywords Vector Point Polyline Polygon Vertex Geometry Scale Data Quality Symbology Data Sources Overview Vector data provide a way to represent real world features within the GIS environment A feature is anything you can see on the landscape Imagine you are st
5. e Area edges of a municipality map must not overlap e Area edges of a municipality map must not have gaps slivers e Polygons showing property boundaries must be closed Undershoots or overshoots of the border lines are not allowed e Contour lines in a vector line layer must not intersect cross each other Topological tools Many GIS applications provide tools for topological editing For example in QGIS you can enable topological editing to improve editing and maintaining common boundaries in polygon layers A GIS such as QGIS detects a shared boundary in a polygon map so you only have to move the edge vertex of one polygon boundary and QGIS will ensure the updating of the other polygon boundaries as shown in Figure 1 Another topological option allows you to prevent polygon overlaps during digitising see Figure 2 2 If you already have one polygon it is possible with this option to digitise a second adjacent polygon so that both polygons overlap and QGIS then clips the second polygon to the common boundary Figure 49 1 Topological editing to detect shared boundaries when moving vertices When moving a vertex all features that share that vertex are updated 2 To avoid polygon overlaps when a new polygon is digitised shown in red it is clipped to avoid overlapping neighbouring areas mE A Gentle Introduction to GIS 58 GIS FOR EDUCATORS Snapping distance Snapping distance is the distance
6. relationship to the areas on the Earth that they represent the map is an equal area map In practice general reference and educational maps most often require the use of equal area projections As the name implies these maps are best used when calculations of area are the dominant calculations you will perform If for example you are trying to analyse a particular area in your town to find out whether it is large enough for a new shopping mall equal area projections are the best choice On the one hand the larger the area you are analysing the more precise your area measures will be if you use an equal area projection rather than another type On the other hand an equal area projection results in distortions of angular conformity when dealing with large areas Small areas will be far less prone to having their angles distorted when you use an equal area projection Alber s Equal A Gentle Introduction to GIS 66 GIS FOR EDUCATORS Area Lambert s Equal Area and Mollweide Equal Area Cylindrical projections shown in Figure 56 are types of equal area projections that are often encountered in GIS work Keep in mind that map projection is a very complex topic There are hundreds of different projections available world wide each trying to portray a certain portion of the earth s surface as faithfully as possible on a flat piece of paper In reality the choice of which projection to use will often be made for you Most countries have c
7. 29 A contour map drawn using continuous colour symbology A Gentle Introduction to GIS 29 3 VECTOR ATTRIBUTE DATA Unique Value Symbols Sometimes the attributes of features are not numeric but instead strings are used String is a computer term meaning a group of letters numbers and other writing symbols Strings attributes are often used to classify things by name We can tell the GIS Application to give each unique string or number its own colour and symbol Road features may have different classes e g street secondary road main road etc each drawn in the map view of the GIS with different colours or symbols This is illustrated in Table 7 Table 7 Unique attribute values for a feature type e g roads can each have their own symbol Attribute Value Colour class and symbol Arterial route Main road Secondary road Within the GIS Application we can open choose to use Unique Value symbology for a layer The GIS will scan through all the different string values in the attribute field and build a list of unique strings or numbers Each unique value can then be assigned a colour and style This is shown in Figure 30 Figure 30 Defining unique value symbology for roads based on the road type Layer Properties General Symbology Metadata Labels Actions Attributes Legend type Unique Value Transparency 0 j Classification field FEAT_TYPE Class
8. GER Soe a 46 WNS TEXT lt lt do da RAS RS OSS A OE Ke REE Sw WR DO 46 5 Raster Data 47 e ooi eh ow ene a a a tee a a ed RC ee ae ag 47 Raster data in detail o o o s sor moa GROSS ERTS O48 a 25 48 Georeferencing a 9 ee e che ok e A A e CS Sed 49 Sources of raster data 6 25 desde Se eee Ride ek OS ER ORE SRO 50 State Resoldio o s bee Sa A ee eG ESO AE oe SRS ESS 51 Spectral resolution sk ew ee nice ee 52 Raster to vector conversion lt lt occ er ewe ee eee SAA ee Sede Ewe ed 53 Vector to raster conversion 6 ee Sha eRe ae ee A oe a ee 53 a s o s e 68 RS hE Re SK EES A Pe See ae SEE eS 53 Common problems things to be aware of 2 2 ee ee ee 54 What have we learned 2224200450884 8488 OES REEDED ESSE VER 54 ROR VOU 32 x ee d 6 35 8 a le SEER SSS BOSE DEGASSED SS 54 Something to think about rea PEt eS Se See Sg eee a 55 Furiher reading e ida a ECR Rae da a See we e bE SS Gwe Bae a 55 Wa SDE di ERA ee ee es A eS Be we aai 55 6 Topology 56 A Gentle Introduction to GIS V Contents COM 2 o pa o ir da io o e ar a de 56 TOPOLOGY ONOS score A OH 57 Topology TINGS s so coag aa A a E oe e a Bs 58 WII IG IS oo ee ale ee ee area ee ee a eee Se ae ee ee A 58 Snapping distance ts ES Sa Be ee pom ra Rs a Se eR ee erecgee peets 59 SP MONS s sa os ek ary Be A LE ae oe BOR ae Kae Re oe ae 59 Common problems things to be awareof 2 0 es 59 What have we leamed ane ks oe BARA EA N A AA 60
9. Type txt Look Out Point Notes Ext View of the lake To capture a polyline the process is similar to that of a point in that you need to first use the pan and zoom tools to move the map in the map view to the correct geographical area You should be zoomed in enough so that your new vector polyline feature will have an appropriate scale see Topic 2 Working with Vector Data for more details on scale issues When you are ready you can click the polyline capture icon in the tool bar and then start drawing your line by clicking on the map After you make your first click you will notice that the line stretches like an elastic band to follow the mouse cursor around as you move it Each time you click with the left mouse button a new vertex will be added to the map This process is shown in Figure 37 When you have finished defining your line use the right mouse button to tell the GIS Application that you have completed your edits As with the procedure for capturing a point feature you will then be asked to enter in the attribute data for your new polyline feature The process for capturing a polygon is almost the same as capturing a polyline except that you need to use the polygon capture tool in the tool bar Also you will notice that when you draw your geometry on the screen the GIS Application always creates an enclosed area To add a new feature after you have created your first one you can simply click again on the map with t
10. You should concentrate on what story you want to tell with your map and how the elements such as the legend scale bar and acknowledgements should be ordered By doing this you will have a well designed and educational map that people would like to look at and be able to understand A Gentle Introduction to GIS 80 GIS FOR EDUCATORS What have we learned Let s wrap up what we covered in this worksheet e Map production means arranging map elements on a sheet of paper Map elements are the title map body map border legend scale north arrow and the acknowl edgement Scale represents the ratio of a distance on the map to the actual distance in the real world Scale is displayed in map units meters feet or degrees A legend explains all the symbols on a map A map should explain complex information as simply as possible Maps are usually always displayed North up Now you try Here are some ideas for you to try with your learners e Load some vector layers in your GIS for your local area See if your learners can identify examples of different types of legend elements such as road types or buildings Create a list of legend elements and define what the icons should look like so a reader can most easily figure out their meaning in the map e Create a map layout with your learners on a sheet of paper Decide on the title of the map what GIS layers you want to show and what colours and icons to have on the m
11. and time required to research and capture the information Very often we obtain vector data from companies friends or the government In these cases it is usually not possible to request specific attributes and we have to make do with what we get A Gentle Introduction to GIS 25 3 VECTOR ATTRIBUTE DATA Single Symbols If a feature is symbolised without using any attribute table data it can only be drawn in a simple way For example with point features you can set the colour and marker circle square star etc but that is all You cannot tell the GIS to draw the features based on one of its properties in the attribute table In order to do that you need to use either a graduated continuous or unique value symbol These are described in detail in the sections that follow A GIS application will normally allow you to set the symbology of a layer using a dialog box such as the one shown in Figure 25a In this dialog box you can choose colours and symbol styles Depending on the geometry type of a layer different options may be shown For example with point layers you can choose a marker style With line and polygon layers there is no marker style option but instead you can select a line style and colour such as dashed orange for gravel roads solid orange for minor roads and so on as shown in 25b With polygon layers you also have the option of setting a fill style and colour Figure 25 Setting the symbology of a vector layer L
12. be drawn g Quantum Gis 1 0 0 Kore Vectors va x Quantum GIS 1 0 0 Kore Vectors va x Ble Edit View Layer Settings Plugins Tools Help Bile Edit View Layer Settings Plugins Tools Help Jada o RRE l a O saaa LEEF T P B nO rnts Ed RRO pad MAZAO PRESBBORR S AAAA gt gt gt B r n2 M rA erxrn0 raD vMarxaqeo Legend JE ae dy Roads ae 1 Road Outlines 3 Inland Waters w E River Areas ae l Rivers Lines ae Contours 4 s Building Points ae Building Areas x E map_50_000 f Spot Heights xx E province_new 3226AA_1996_ED3_GEO xx E boundary D 0 9 8 5 0 0 5 8 8 8 Bh N de o 0 005 4 Legend GE degrees x Road Outlines 8 Inland Waters xx River Areas ae ly Rivers Lines 28d Contours 2 is Building Points ax Building Areas x map 50_000 Is Spot Heights xx province_new 3226AA_1996_ED3_GEO xx boundary T 0 1 Roads aa p p p P P 0 P P P P P P H 1205 LON aGIS 2009 wea a gt PATEAR S 9 o ooo degrees 205 aGIS 2009 There s a plugin update avalabte QB 26 07200 32 08620 Scale 1 9136 0 2 Render i F There is a plugin update avatable 5 _26 09044 3207818_ Scaie 1 9135 Oe ree ig b When a layer for example the trees layer above is first loaded a GIS application will give it a generic symbol see that our po
13. create buffer zones around buildings Make small pencil marks at equal distance all along your feature using the compass then connect the marks using a ruler Further reading Books e Galati Stephen R 2006 Geographic Information Systems Demystified Artech House Inc ISBN 158053533X e Chang Kang Tsung 2006 Introduction to Geographic Information Systems 3rd Edition Mc Graw Hill ISBN 0070658986 e DeMers Michael N 2005 Fundamentals of Geographic Information Systems 3rd Edition Wiley ISBN 9814126195 Websites http www manifold net doc transform_border_buffers htm The QGIS User Guide also has more detailed information on analysing vector data in QGIS A Gentle Introduction to GIS 89 9 VECTOR SPATIAL ANALYSIS BUFFERS What s next In the section that follows we will take a closer look at interpolation as an example of spatial analysis you can do with raster data A Gentle Introduction to GIS 90 GIS FOR EDUCATORS 10 Spatial Analysis Interpolation Objectives Understanding of interpolation as part of spatial analysis Keywords Point data interpolation method In verse Distance Weighted Triangu lated Irregular Network Overview Spatial analysis is the process of manipulating spatial information to extract new information and meaning from the original data Usually spatial analysis is carried out with a Geographic Information System GIS A GIS usually provides spa
14. e ha e pS o wee A a d x aGis 2009 Figure 6 Changing the layer order allows to adjust the way that layers are drawn v amp Roads 1 1mil Outlines C HIGHWAY MAIN ROADS 3 VI e Roads 1 15k Outlines H VI amp Railways s Places QGIS 2009 5 Scale 132380 68 v Render fig A HIGHWAY MAIN ROADS le Roads 1 1mil Outlines HIGHWAY MAIN ROADS MI X _ Roads 1 15k amp Roads 1 15k Outlines QGIs 2009 le 1 32380 Render im a Before changing the layer order rivers are drawn underneath roads b After changing the layer order rivers are drawn on top of roads Getting a GIS Application for your own computer s There are many different GIS Applications available Some have many sophisticated features and cost tens of thousands of Rands for each copy In other cases you can obtain a GIS Application for free Deciding which GIS Application to use is a question of how much money you can afford and personal preference For these tutorials we will be using the Quantum GIS Application also known as QGIS Quantum GIS is completely free and you can copy it and share it with your friends as much as you like If you received this tutorial in printed form you should have received a copy of QGIS with it If not you can always visit http qgis org to download your free c
15. give the shapefile a short and meaningful name Good examples are rivers watersamples and so on Let s recap the process again quickly To create a shapefile you first say what kind of geometry it will hold then you create one or more fields for the attribute table and then you save the shapefile to the hard disk using an easy to recognise name Easy as 1 2 3 A Gentle Introduction to GIS 38 GIS FOR EDUCATORS Figure 35 After defining our new layer s geometry and attributes we need to save it to disk It is important to give a short but meaningful name to your shapefile Look im F amosen Files I5igisdatallocal _ o gt 4 ca 9 My Computer El SO0k_riversa shp 50k_spothgt shx E 50k_riversa shx boundary dbf J Administrator 50k_roads dbf boundary prj boundary gml boundary shp boundary shx elevation_p1000 dbf elevation_p1000 prj elevation_p1000 qml elevation_p1000 shp elevation_p1000 shx houses dbf houses prj houses qml 50k_roads prj 50k_roads qml Z 50k_roads shp 5O0k_roads shx 50k_roads_pg qml 3 S0k_roads_pg qmle E 50k_roadsoutline qml SOk_spothat dbf E SOk_spothat prj BU EVEN EYEE el E S0k_spothat qml 50k_spothgt shp LET BUCH BUCH BUCH BUCH BUG BUCH B File name tourism_points shp Files of type All Files ds Cancel Encoding Systemi izj Adding data to your shapefile So
16. have temperature rainfall and wind strength data and ask you to interpolate their data to estimate places where tourists will probably have optimal weather conditions with mild temperatures no rainfall and little wind strength Can you identify the areas in your region that meet these criteria Something to think about If you don t have a computer available you can use a toposheet and a ruler to estimate elevation values between contour lines or rainfall values between fictional weather stations For example if rainfall at weather station A is 50 mm per month and at weather station B it is 90 mm you can estimate that the rainfall at half the distance between weather station A and B is 70 mm Further reading Books e Chang Kang Tsung 2006 Introduction to Geographic Information Systems 3rd Edition Mc Graw Hill ISBN 0070658986 e DeMers Michael N 2005 Fundamentals of Geographic Information Systems 3rd Edition Wiley ISBN 9814126195 e Mitas L Mitasova H 1999 Spatial Interpolation In P Longley M F Goodchild D J Maguire D W Rhind Eds Geographical Information Systems Principles Techniques Man agement and Applications Wiley Websites http en wikipedia org wiki Interpolation http en wikipedia org wiki Delaunay_triangulation http www agt bme hu public_e funcint funcint html The QGIS User Guide also has more detailed information on interpolation tools provided in QGIS A Gentle In
17. in an otherwise Transparent file format whose markup or absence of markup has been arranged to thwart or discourage subsequent modification by readers is not Transparent An image format is not Transparent if used for any substantial amount of text A copy that is not Transparent is called Opaque Examples of suitable formats for Transparent copies include plain ASCII without markup Texinfo input format IATEX input format SGML or XML using a publicly available DTD and standard conforming simple HTML PostScript or PDF designed for human modification Examples of transparent image formats include PNG XCF and JPG Opaque formats include proprietary formats that can be read and edited only by proprietary word processors SGML or XML for which the DTD and or processing tools are not generally available and the machine generated HTML PostScript or PDF produced by some word processors for output purposes only The Title Page means for a printed book the title page itself plus such following pages as are needed to hold legibly the material this License requires to appear in the title page For works in formats which do not have any title page as such Title Page means the text near the most prominent appearance of the work s title preceding the beginning of the body of the text A section Entitled XYZ means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following
18. in important parts of the wetland being left out of the reserve On the other hand if you are trying to create a regional map using data captured at 1 1000 000 might be just fine and will save you a lot of time and effort capturing the data Figure 13 Maps with different scales g Quantum Gis 1 0 0 Kore EasternCapeScaleDifferences va x Quantum Gis 1 0 0 Kore EasternCapeScaleDifferences va Ble Edit View Layer Settings Plugins Tools Help Ble Edit View Layer Settings Plugins Tools Help igsgB2 ea4skee erg UB ESO aaee Pe Ue o OLADIA PA KREQGOPhRR MAAA Z2 uUNO ante x Q0F BR MAA gt EBaaxraneo PRERSORR S gt o Maaraaeo KYPRARESORR amp Legend ax E 88 vmap countries Legend 8 2 a 8 Ss vmap_countries NASA JPL S NASA JPL oe There is plugin update avaiable QS _15 1248 33 1445 Scale 1 50000 0 2 Rener i A There s a plugin update avadabie QB 18 0525 33 1349 Scale 1 50000 0 Render i P a Vector data red lines that was digitised from a b Vector data green lines that was digitised from a small scale 1 1000 000 map large scale 1 50 000 map Symbology When you add vector layers to the map view in a GIS application they will be drawn with random colours and basic symbols One of the great advantages of using a GIS is that you can create personalised maps very easily The GIS program will let you choose colours to suite the feature type e g you c
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21. quick and easy In Figure 23 you can see an example of an attribute search in a GIS Finally attribute data can be very useful in carrying out spatial analysis Spatial analysis combines the spatial information stored in the geometry of features with their attribute information This allows us to study features and how they relate to each other There are many types of spatial analysis that can be carried out for example you could use GIS to find out how many red roofed houses occur in a particular area If you have tree features you could use GIS to try to find out which species might be affected if a piece of land is developed We can use the attributes stored for water samples along a river course to understand where pollution is entering into the stream The possibilities are endless In a later topic we will be exploring spatial analysis in more detail Before we move on to attribute data in more detail let s take a quick recap Features are real world things such as roads property boundaries electrical substation sites and so on A feature has a geometry which determines if it is a point polyline or polygon and attributes which describe the feature This is shown in Figure 24 A Gentle Introduction to GIS 23 3 VECTOR ATTRIBUTE DATA Figure 23 In a GIS Application we can also search for features based on their attributes Here we see a search for houses with black roofs Results are shown in yellow in the map turquoise on
22. text that translates XYZ in another language Here XYZ stands for a specific section name mentioned below such as Acknowledgements Dedica A Gentle Introduction to GIS 100 GIS FOR EDUCATORS tions Endorsements or History To Preserve the Title of such a section when you modify the Document means that it remains a section Entitled XYZ according to this definition The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document These Warranty Disclaimers are considered to be included by reference in this License but only as regards disclaiming warranties any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License VERBATIM COPYING You may copy and distribute the Document in any medium either commercially or noncommercially provided that this License the copyright notices and the license notice saying this License applies to the Document are reproduced in all copies and that you add no other conditions whatsoever to those of this License You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute However you may accept compensation in exchange for copies If you distribute a large enough number of copies you must also follow the conditions in section 10 You may also lend copies under the same conditions sta
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24. the table g Quantum GIS 1 0 2 Kore EasternCapeVectors File Edit View Layer Plugins Tools Tools Help Jaad RRPLPO KEKER L e ULLOI ARRO ee od eM2X 2080 RE oer rad a Y gt oe oe Jlea lx Legend ES o 0 005 La Black Red vi Building Points v Trees 9 384 YE Roads amp Road Outlines REY lt Y water Bodies gt K Rivers vi Spot Height y aor 9 viik Contours t Ch v Building Areas Y 7 River Areas 0 QGIS 2009 There is a new plugin available 26 07573 32 09474 Scale 1 17067 3 Render iz ol Attribute table houses L JLo bx aaggga id RoofColour HasBalcony DateBullt 2 1 0 Red 1 2000 2 1 Black 1 2008 3 2 Red 1 2001 H EE E Search for Black in RoofColour lt Search select Advanced Q Help EJ Close ll A Figure 24 Vector features at a glance Attributes A Gentle Introduction to GIS 24 GIS FOR EDUCATORS Attributes in detail Attributes for a vector feature are stored in a table A table is like a spreadsheet Each column in the table is called a field Each row in the table is a record Table 4 shows a simple example of how an attribute table looks in a GIS The records in the attribute table in a GIS each correspond to one feature Usually the information in the attribute table is stored in some kind of database The GIS application links the attribute records with the feature
25. themes In Figure 62 you can see a map with a lake in light blue overlaid with contour lines and spot heights to show information about the terrain in that area On the right side you see the same area with the lake in the background but this map is designed to show tourists the location of houses they can rent for their holidays It uses brighter colours a house icon and more descriptive and inviting words in the legend North arrow in detail A north arrow sometimes also called a compass rose is a figure displaying the main directions North South East and West On a map it is used to indicate the direction of North For example in GIS this means that a house that is located north from a lake can be found on top of the lake on a map The road in the east will then be to the right of the water body on the map a river in the south will be below the water body and if you are searching for a train station to the west of the lake you will find it on the left side on the map Scale in detail The scale of a map is the value of a single unit of distance on the map representing distance in the real world The values are shown in map units meters feet or degrees The scale can be expressed in several ways for example in words as a ratio or as a graphical scale bar see Figure 63 Expressing a scale in words is a commonly used method and has the advantage of being easily understood by most map users You can see an example of a word based sca
26. to special receiving stations such as the one shown in Figure 44 The process of capturing raster data from an aeroplane or satellite is called remote sensing Figure 44 The CSIR Satellite Applications Center at Hartebeeshoek near Johannesburg Special antennae track satellites as they pass overhead and download images using radio waves In other cases raster data can be computed For example an insurance company may take police crime incident reports and create a country wide raster map showing how high the incidence of crime is likely to be in each area Meteorologists people who study weather patterns might generate a province level raster showing average temperature rainfall and wind direction using data collected from weather stations see Figure 44 In these cases they will often use raster analysis techniques such as interpolation which we describe in Topic 10 Sometimes raster data are created from vector data because the data owners want to share the data in an easy to use format For example a company with road rail cadastral and other vector datasets may choose to generate a raster version of these datasets so that employees can view these datasets in a web browser This is normally only useful if the attributes that users need to be aware of can be represented on the map with labels or symbology If the user needs to look at the attribute table for the data providing it in raster format could be a bad choice because raster
27. under this License provided you insert a copy of this License into the extracted document and follow this License in all other respects regarding verbatim copying of that document AGGREGATION WITH INDEPENDENT WORKS A compilation of the Document or its derivatives with other separate and independent documents or works in or on a volume of a storage or distribution medium is called an aggregate if the copyright resulting from the compilation is not used to limit the legal rights of the compilation s users beyond what the individual works permit When the Document is included in an aggregate this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document If the Cover Text requirement of section 10 is applicable to these copies of the Document then if the Document is less than one half of the entire aggregate the Document s Cover Texts may be placed on covers that bracket the Document within the aggregate or the electronic equivalent of covers if the Document is in electronic form Otherwise they must appear on printed covers that bracket the whole aggregate A Gentle Introduction to GIS 104 GIS FOR EDUCATORS TRANSLATION Translation is considered a kind of modification so you may distribute translations of the Document under the terms of section 10 Replacing Invariant Sections with translations requires special permis sion from their copyright holders but you
28. values in different value ranges The GIS Application will analyse the attribute data e g height and based on the number of classes you request create groupings for you This process is illustrated in Table 5 A Gentle Introduction to GIS 27 3 VECTOR ATTRIBUTE DATA Table 5 Graduated colour breaks up the attribute value ranges into the number of classes you select Each class is represented by a different colour Attribute Value O vo EN 77 o o gt Q e e c O CO Y O OI AJOIN Continuous Colour Symbols In the previous section on Graduated Colour symbols we saw that we can draw features in discrete groups or classes Sometimes it is useful to draw features in a colour range from one colour to another The GIS Application will use a numerical attribute value from a feature e g contour heights or pollution levels in a stream to decide which colour to use Table 6 shows how the attribute value is used to define a continuous range of colours Table 6 Continuous colour symbology uses a start colour e g light orange shown here and an end colour e g dark brown shown here and creates a series of shades between those colours Attribute Value Colour no classes or grouping O0O O J DO OI B 0O N Using the same contours example we used in the previous section let s see how a map with contin uous co
29. with us Sibongile Mthombeni Sibongile lives near Johannesburg with her young daughter Her goal is to continue her studies and become a nurse Working on this project was the first time Sibongile used a computer GIS FOR EDUCATORS GNU Free Documentation License Version 1 2 November 2002 Copyright 2000 2001 2002 Free Software Foundation Inc 59 Temple Place Suite 330 Boston MA 02111 1307 USA Everyone is permitted to copy and distribute verbatim copies of this license document but changing it is not allowed PREAMBLE The purpose of this License is to make a manual textbook or other functional and useful document free in the sense of freedom to assure everyone the effective freedom to copy and redistribute it with or without modifying it either commercially or noncommercially Secondarily this License preserves for the author and publisher a way to get credit for their work while not being considered responsible for modifications made by others This License is a kind of copyleft which means that derivative works of the document must them selves be free in the same sense lt complements the GNU General Public License which is a copyleft license designed for free software We have designed this License in order to use it for manuals for free software because free software needs free documentation a free program should come with manuals providing the same freedoms that the software does But this
30. you should put a lot of thought into how you symbolise your maps in order to make them easy to understand What have we learned Let s wrap up what we covered in this worksheet e Vector features have attributes e Attributes describe the properties of the feature e The attributes are stored in a table e Rows in the table are called records e There is one record per feature in the vector layer e Columns in the table are called fields e Fields represent properties of the feature e g height roof colour etc e Fields can contain numerical string any text and date information e The attribute data for a feature can be used to determine how it is symbolised A Gentle Introduction to GIS 31 3 VECTOR ATTRIBUTE DATA e Graduated colour symbology groups the data into discrete classes e Continuous colour symbology assigns colours from a colour range to the features based on their attributes e Unique value symbology associates each different value in the chosen attribute column with a different symbol colour and style e f the attribute of a vector layer is not used to determine its symbology it is drawn using a single symbol only Now you try Here are some ideas for you to try with your learners e Using the table that you created in the last topic add a new column for the symbology type you would use for each feature type and have the learners identify which symbology type they would use see Table 8 for an example
31. A Gentle Introduction to GIS Brought to you with Quantum GIS a Free and Open Source Software GIS Application for everyone T Sutton O Dassau M Sutton sponsored by Chief Directorate Spatial Planning amp Information Department of Land Affairs Eastern Cape South Africa in partnership with Spatial Information Management Unit Office of the Premier Eastern Cape South Africa 27 Province of the MISA EASTERN CAPE L OFFICE OF THE PREMIER Copyright information Copyright 2009 Chief Directorate Spatial Planning amp Information Department of Land Affairs Eastern Cape Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 2 or any later version pub lished by the Free Software Foundation with no Invariant Sections no Front Cover Texts and no Back Cover Texts A copy of the license is included in section 10 entitled GNU Free Documentation License The above copyright notice excludes the QGIS User Manual which may be appended to this document Consult the QGIS Manuals for further copyright and licensing infor mation A word from the editor This project was sponsored by the Chief Directorate Spatial Planning amp Information Department of Land Affairs DLA Eastern Cape in conjunction with the Spatial Information Management Unit Office of the Premier Eastern Cape South Africa GIS is becoming an increasi
32. ASTER DATA Raster data in detail Raster data is used in a GIS application when we want to display information that is continuous across an area and cannot easily be divided into vector features When we introduced you to vector data we showed you the image in Figure 42 Point polyline and polygon features work well for representing some features on this landscape such as trees roads and building footprints Other features on a landscape can be more difficult to represent using vector features For example the grasslands shown have many variations in colour and density of cover It would be easy enough to make a single polygon around each grassland area but a lot of the information about the grassland would be lost in the process of simplifying the features to a single polygon This is because when you give a vector feature attribute values they apply to the whole feature so vectors aren t very good at representing features that are not homogeneous entirely the same all over Another approach you could take is to digitise every small variation of grass colour and cover as a separate polygon The problem with that approach is that it will take a huge amount of work in order to create a good vector dataset Figure 42 Some features on a landscape are easy to represent as points polylines and polygons e g trees roads houses In other cases it can be difficult For example how would you represent the grasslands As polygons What about the
33. License is not limited to software manuals it can be used for any textual work regardless of subject matter or whether it is published as a printed book We recommend this License principally for works whose purpose is instruction or reference APPLICABILITY AND DEFINITIONS This License applies to any manual or other work in any medium that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License Such a notice grants a world wide royalty free license unlimited in duration to use that work under the conditions stated herein The Document below refers to any such manual or work Any member of the public is a licensee and is addressed as you You accept the license if you copy modify or distribute the work in a way requiring permission under copyright law A Modified Version of the Document means any work containing the Document or a portion of it either copied verbatim or with modifications and or translated into another language A Gentle Introduction to GIS 99 10 SPATIAL ANALYSIS INTERPOLATION A Secondary Section is a named appendix or a front matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document s overall subject or to related matters and contains nothing that could fall directly within that overall subject Thus if the Document is in part a textbook of mathemat
34. R TITLES with the Front Cover Texts being LIST and with the Back Cover Texts being LIST If you have Invariant Sections without Cover Texts or some other combination of the three merge those two alternatives to suit the situation If your document contains nontrivial examples of program code we recommend releasing these examples in parallel under your choice of free software license such as the GNU General Public License to permit their use in free software A Gentle Introduction to GIS 106
35. RI Table 3 Create a table like this leaving the geometry type column empty and ask your learners to decide on suitable geometry types Real world feature Suitable Geometry Type The school flagpole The soccer field The footpaths in an around the school Places where taps are located Etc A Gentle Introduction to GIS 19 2 VECTOR DATA Something to think about If you don t have a computer available you can use a toposheet and transparency sheets to show your learners about vector data Further reading The QGIS User Guide also has more detailed information on working with vector data in QGIS What s next In the section that follows we will take a closer look at attribute data to see how it can be used to describe vector features A Gentle Introduction to GIS 20 GIS FOR EDUCATORS 3 Vector Attribute Data Objectives In this topic we describe how at tribute data are associated with vector features and can be used to symbolise data Keywords Attribute database fields data vector symbology Overview If every line on a map was the same colour width thickness and had the same label it would be very hard to make out what was going on The map would also give us very little information Take a look at Figure 19 below for example Figure 19 Maps come to life when colour and different symbols are used to help you to tell one type of feature from the next Can you
36. S 54 GIS FOR EDUCATORS Something to think about If you don t have a computer available you can understand raster data using pen and paper Draw a grid of squares onto a sheet of paper to represent your soccer field Fill the grid in with numbers representing values for grass cover on your soccer field If a patch is bare give the cell a value of O If the patch is mixed bare and covered give it a value of 1 If an area is completely covered with grass give it a value of 2 Now use pencil crayons to colour the cells based on their values Colour cells with value 2 dark green Value 1 should get coloured light green and value 0 coloured in brown When you finish you should have a raster map of your soccer field Further reading Book Chang Kang Tsung 2006 Introduction to Geographic Information Systems 3rd Edition McGraw Hill ISBN 0070658986 DeMers Michael N 2005 Fundamentals of Geographic Information Sys tems 3rd Edition Wiley ISBN 9814126195 Website http en wikipedia org wiki GIS Raster The QGIS User Guide also has more detailed information on working with raster data in QGIS What s next In the section that follows we will take a closer look at topology to see how the relationship between vector features can be used to ensure the best data quality A Gentle Introduction to GIS 55 6 TOPOLOGY 6 Topology Objectives Understanding topology in vector data Keywords Vector toplology
37. SSA ecs sa ae me ee Gr Ce ee ee Se Ae ree Gaeta E 60 Something to think about 2 ch wea wa a eee eee e BS 60 Further PEGGING s e c eo cnica hb 4 G44 a dd 60 Whats nakl 200023324 G49 6 545329 E6842 ERE ERAS GAEDE de DE CH 61 7 Coordinate Reference Systems 62 Overview ee che ia ed eh ce Ke A AA Sa 62 Map Projection in detail lt lt anne ce bed we de eee wee ee ee ee da we de 62 The three families of map projections 2 20 ee ee 63 Accuracy Of map projechons c c tacs si eee Re we Ea le OA awe 64 Map projections with angular conformity 0 2 00 eee ee eee 64 Map projections with equal distance 02 0000 eee ee es 65 Projections with equal areas ee 66 Coordinate Reference System CRS in detail o eee 67 Geographic Coordinate Systems lt co0os2o on eres a 67 Projected coordinate reference systems eee ee ee es 69 Universal Transverse Mercator UTM CRS in detail 70 On The Fly Projection c c 2c kaw Gee ee ee A A RR e BS 72 Common problems things tobe awareof 2 0 ee es 72 Vinal Nave we leamed ok eso ae OS GEA CREAR EE EHD WADE YA OH 72 Now you tyl s eh oe CR a SES toe we Oe a Bow as 73 Something to think about ots pidio bee ee eee ee eee Ee eee dee 73 FUN reading 6 2 za ido be Se ee o a add Ad E Te 73 SMS scada a id AER A 74 8 Map Production 75 COMIC lt p ara A A A A A A A a ea 75 Map TIE ILUSION a ecni a a a a
38. WNA SNET ohhh E a ee Re a da ES 90 10 Spatial Analysis Interpolation 91 SST oo sac se ES 8 ee we we he BM OE ES a 91 Spatial interpolation in detail ooa oaa ee ee 91 Inverse Distance Weighted IDW 2 2 66 ee eee bee ee ee ee eS 92 Triangulated Irregular Network TIN 2 2 00 2 eee ee 93 Common problems things to be aware of 2 e 95 Other interpolation methods aooo Se we 95 What have we learned soo sone dore taor ekot e A we 95 Now VOU 625656 sde dd AR A a 96 Something to think about cromos rra BSG Oe A A A A Sows 96 FUNES ys cer edo nda ri 96 AUS IE aa A AA A a OR A hae Be a 97 Authors and Contributors 98 GNU Free Documentation License 99 A Gentle Introduction to GIS vil GIS FOR EDUCATORS 1 Introducing GIS Objectives Understanding what GIS is and what it can be used for Keywords GIS Computer Maps Data Infor mation System Spatial Analysis Overview Just as we use a word processor to write documents and deal with words on a computer we can use a GIS application to deal with spatial information on a computer GIS stands for Geographical Information System A GIS consists of e Digital Data the geographical information that you will view and analyse using computer hard ware and software e Computer Hardware computers used for storing data displaying graphics and processing data e Computer Software computer programs that run on the computer hardwa
39. You would also need to make a map reading of your position or obtain your position using a GPS receiver To store the data collected from an exercise like this in a GIS Application you would probably create a GIS layer with a point geometry Using point geometry makes sense here because each sample taken represents the conditions at a very specific place For the attributes we would want a field for each thing that describes the sample site So we may end up with an attribute table that looks something like Table 10 Table 10 Drawing a table like this before you create your vector layer will let you decide what attribute fields columns you will need Note that the geometry positions where samples were taken is not shown in the attribute table the GIS Application stores it separately SampleNo pH DO CB Turbidity Collector Date 1 7 6 N Low Patience 12 01 2009 2 6 8 5 Y Medium Thabo 12 01 2009 3 6 9 6 Y High Victor 12 01 2009 Creating an empty shapefile Once you have planned what features you want to capture into the GIS and the geometry type and attributes that each feature should have you can move on to the next step of creating an empty shapefile The process usually starts with choosing the new vector layer option in your GIS Application and then selecting a geometry type see Figure 34 As we covered in an earlier topic this means choosing either point polyline or polygon for the geometry
40. a GIS uses to search for the closest vertex and or segment you are trying to connect when you digitise A segment is a straight line formed between two vertices in a polygon or polyline geometry If you aren t within the snapping distance a GIS such as QGIS will leave the vertex where you release the mouse button instead of snapping it to an existing vertex and or segment see Illustration 4 below Figure 50 The snapping distance black circle is defined in map units e g decimal degrees for snapping to either vertices or segments vartan Line Segment Snapping Distance Snapping Distance Search Radius Search radius is the distance a GIS uses to search for the closest vertex you are trying to move when you click on the map If you aren t within the search radius the GIS won t find and select any vertex of a feature for editing In principle it is quite similar to the snapping distance functionality Snapping distance and search radius are both set in map units so you may need to experiment to get the distance value set right If you specify a value that is too big the GIS may snap to a wrong vertex especially if you are dealing with a large number of vertices close together If you specify the search radius too small the GIS application won t find any feature or vertex to move or edit Common problems things to be aware of Topology is a complex representation of vector data True topological vector datase
41. al analy sis buffer distance dissolve bound ary outward and inward buffer mul tiple buffer Overview Spatial analysis uses spatial information to extract new and additional meaning from GIS data Usually spatial analysis is carried out using a GIS Application GIS Applications normally have spatial analysis tools for feature statistics e g how many vertices make up this polyline or geoprocessing such as feature buffering The types of spatial analysis that are used vary according to subject areas People working in water management and research hydrology will most likely be interested in analysing terrain and modelling water as it moves across it In wildlife management users are interested in analytical functions that deal with wildlife point locations and their relationship to the environment In this topic we will discuss buffering as an example of a useful spatial analysis that can be carried out with vector data Buffering in detail Buffering usually creates two areas one area that is within a specified distance to selected real world features and the other area that is beyond The area that is within the specified distance is called the buffer zone A buffer zone is any area that serves the purpose of keeping real world features distant from one another Buffer zones are often set up to protect the environment protect residential and commercial zones from industrial accidents or natural disasters or to prevent violence Co
42. al density of information used to create the raster will usually determine the spatial resolution For example if you want to create a high resolution average rainfall map you would ideally need many weather stations in close proximity to each other One of the main things to be aware of with rasters captured at a high spatial resolution is storage requirements Think of a raster that is 3x3 pixels each of which contains a number representing average rainfall To store all the information contained in the raster you will need to store 9 numbers in the computer s memory Now imagine you want to have a raster layer for the whole of South Africa with pixels of 1km x 1km South Africa is around 1 219 090 km2 Which means your computer would need to store over a million numbers on its hard disk in order to hold all of the information Making the pixel size smaller would greatly increase the amount of storage needed Sometimes using a low spatial resolution is useful when you want to work with a large area and are not interested in looking at any one area in a lot of detail The cloud maps you see on the weather report are an example of this it s useful to see the clouds across the whole country Zooming in to one particular cloud in high resolution will not tell you very much about the upcoming weather On the other hand using low resolution raster data can be problematic if you are interested in a small region because you probably won t be able to
43. an be represented by a cylindrical projections b conical projections or c planar projections das UE NWE A Gentle Introduction to GIS 63 7 COORDINATE REFERENCE SYSTEMS Accuracy of map projections Map projections are never absolutely accurate representations of the spherical earth As a result of the map projection process every map shows distortions of angular conformity distance and area A map projection may combine several of these characteristics or may be a compromise that distorts all the properties of area distance and angular conformity within some acceptable limit Examples of compromise projections are the Winkel Tripel projection and the Robinson projection see Figure 52 which are often used for world maps Figure 52 The Robinson projection is a compromise where distortions of area angular conformity and dis tance are acceptable It is usually impossible to preserve all characteristics at the same time in a map projection This means that when you want to carry out accurate analytical operations you need to use a map pro jection that provides the best characteristics for your analyses For example if you need to measure distances on your map you should try to use a map projection for your data that provides high accu racy for distances Map projections with angular con
44. an tell it to draw a water bodies vector layer in blue The GIS will also let you adjust the symbol used So if you have a trees point layer you can show each tree position with a small picture of a tree rather than the basic circle marker that the GIS uses when you first load the layer see Figure 14 Symbology is a powerful feature making maps come to life and the data in your GIS easier to un derstand In the topic that follows working with attribute data we will explore more deeply how symbology can help the user to understand vector data A Gentle Introduction to GIS 14 GIS FOR EDUCATORS Figure 14 How can you adjust the symbology of vector features g Layer Properties ERES General Symbology Metadata Labels Actions Attributes Legend type Single Symbol y Transparency 0 Label Point Symbol QUo0 xAL Ar 1 P OGGG8500000HA iamo o LKe2nr7AGR vs TOSSCSOGOZOHS 6O1t0F OATEFPOVDOSOBOSBIGSR XXX X XOSD ti a Pua BNELKSATNESORO SS a 006 z Rotation field Area scale field Size Lisette y seas Ba 2 00 Style Options Outline style Solid Line JE Outline color st Outline width 0 26 Fill style mm Solid gt E Restore Default Style Save As Default Load Style Save Style Help Apply Cancel a In the GIS you can use a panel like the one above to adjust how features in your layer should
45. and casual users As we described above GIS A Gentle Introduction to GIS 2 GIS FOR EDUCATORS is more than just software it refers to all aspects of managing and using digital geographical data In the tutorials that follow we will be focusing on GIS Software What is GIS Software a GIS Application You can see an example of what a GIS Application looks like in Figure 1 above GIS Applications are normally programs with a graphical user interface that can be manipulated using the mouse and keyboard The application provides menus near to the top of the window File Edit etc which when clicked using the mouse show a panel of actions These actions provide a way for you to tell the GIS Application what you want to do For example you may use the menus to tell the GIS Application to add a new layer to the display output Figure 2 Application menus when clicked with the mouse expand to show a list of actions that can be carried out file Edit View L Plugins Tools Help amp Add Raster Layer SL Bye Add PostGIS Layer Legend 40 Add WMS Layer Open Attribute Tabie We Add to Overview o Add All to Overview Remove All From Overview Q Hide All Layers H Show All Layers s Toolbars rows of small pictures that can be clicked with the mouse normally sit just below the menus and provide a quicker way to use frequently needed actions Figure 3 Toolbars provide quick access to commo
46. and editing vector data is an important function of a GIS since it is one of the main ways in which you can create personal data for things you are interested in Say for example you are monitoring pollution in a river You could use the GIS to digitise all outfalls for storm water drains as point features You could also digitise the river itself as a polyline feature Finally you could take readings of pH levels along the course of the river and digitise the places where you made these readings as a point layer As well as creating your own data there is a lot of free vector data that you can obtain and use For example you can obtain vector data that appears on the 1 50 000 map sheets from the Chief Directorate Surveys and Mapping Scale and vector data Map scale is an important issue to consider when working with vector data in a GIS When data is captured it is usually digitised from existing maps or by taking information from surveyor records and global positioning system devices Maps have different scales so if you import vector data from A Gentle Introduction to GIS 13 2 VECTOR DATA a map into a GIS environment for example by digitising paper maps the digital vector data will have the same scale issues as the original map This effect can be seen in Figure 13 Many issues can arise from making a poor choice of map scale For example using the vector data in Figure 13a to plan a wetland conservation area could result
47. anding on the top of a hill Looking down you can see houses roads trees rivers and so on see Figure 9 Each one of these things would be a feature when we represent them in a GIS Application Vector features have attributes which consist of text or numerical information that describe the features Figure 9 Looking over a landscape you can see the main features such as roads houses and trees A vector feature has its shape represented using geometry The geometry is made up of one or more interconnected vertices A vertex describes a position in space using an x y and optionally z A Gentle Introduction to GIS 9 2 VECTOR DATA axis Geometries which have vertices with a z axis are often referred to as 2 5D since they describe height or depth at each vertex but not both When a feature s geometry consists of only a single vertex it is referred to as a point feature see Figure 10a Where the geometry consists of two or more vertices and the first and last vertex are not equal a polyline feature is formed see Figure 10b Where four or more vertices are present and the last vertex is equal to the first an enclosed polygon feature is formed see Figure 10c Figure 10 Vector point polyline and polygon geometries Vector Point Feature Vector Polyline Feature Vector Polygon Feature Point Geometry indicates the x y and z position of the feature X axis SIXB A Id Name Description Point a
48. ap Use the techniques you learned in Topics 2 and 3 to adjust the symbology accordingly When you have a template open the QGIS Map Composer and try to arrange a map layout as planned Something to think about If you don t have a computer available you can use any topographical map and discuss the map design with your learners Figure out if they understand what the map wants to tell What can be improved How accurately does the map represent the history of the area How would a map from 100 years ago differ from the same map today Further reading Books A Gentle Introduction to GIS 81 8 MAP PRODUCTION e Chang Kang Tsung 2006 Introduction to Geographic Information Systems 3rd Edition Mc Graw Hill ISBN 0070658986 e DeMers Michael N 2005 Fundamentals of Geographic Information Systems 3rd Edition Wiley ISBN 9814126195 Websites http en wikipedia org wiki Scale_ map http www colorado edu geography gcraft notes mapproj mapproj html The QGIS User Guide also has more detailed information on map production provided in QGIS What s next In the section that follows we will take a closer look at vector analysis to see how we can use a GIS for more than just making good looking maps A Gentle Introduction to GIS 82 GIS FOR EDUCATORS 9 Vector Spatial Analysis Buffers Objectives Understanding the use of buffering in vector spatial analysis Keywords Vector buffer zone spati
49. arch QGIS 2009 Georeferencing Georeferencing is the process of defining exactly where on the earth s surface an image or raster dataset was created This positional information is stored with the digital version of the aerial photo When the GIS application opens the photo it uses the positional information to ensure that the photo appears in the correct place on the map Normally this positional information consists of a coordinate for the top left pixel in the image the size of each pixel in the X direction the size of each pixel in the Y direction and the amount if any by which the image is rotated With these few pieces of information the GIS application can ensure that raster data are displayed in the correct place The georeferencing information for a raster is often provided in a small text file accompanying the raster A Gentle Introduction to GIS 49 5 RASTER DATA Sources of raster data Raster data can be obtained in a number of ways Two of the most common ways are aerial pho tography and satellite imagery In aerial photography an aeroplane flies over an area with a camera mounted underneath it The photographs are then imported into a computer and georeferenced Satellite imagery is created when satellites orbiting the earth point special digital cameras towards the earth and then take an image of the area on earth they are passing over Once the image has been taken it is sent back to earth using radio signals
50. ark Corner Westminster St James s Lambeth Park North Bed Victoria amp O Elephant Castle hh O Earl s Sloane Court Square Pimlico 1km A Gentle Introduction to GIS 56 GIS FOR EDUCATORS Topology errors There are different types of topological errors and they can be grouped according to whether the vector feature types are polygons or polylines Topological errors with polygon features can include unclosed polygons gaps between polygon borders or overlapping polygon borders A common topo logical error with polyline features is that they do not meet perfectly at a point node This type of error is called an undershoot if a gap exists between the lines and an overshoot if a line ends beyond the line it should connect to see Figure 48 Figure 48 Undershoots 1 occur when digitised vector lines that should connect to each other don t quite touch Overshoots 2 happen if a line ends beyond the line it should connect to Slivers 3 occur when the vertices of two polygons do not match up on their borders The result of overshoot and undershoot errors are so called dangling nodes at the end of the lines Dangling nodes are acceptable in special cases for example if they are attached to dead end streets Topological errors break the relationship between features These errors need to be fixed in order to be able to analyse vector data with procedures like netw
51. at a topographical map of your town it would be useful to know when the map was created and who did it If the map is already 50 years old you will probably find a lot of houses and roads that no longer exist or maybe never even existed If you Know that the map was created by an official institution you could contact them and ask if they have a more current version of that map with updated information Graticule in detail A graticule is a network of lines overlain on a map to make spatial orientation easier for the reader The lines can be used as a reference As an example the lines of a graticule can represent the earth s parallels of latitude and meridians of longitude When you want to refer to a special area on a map during your presentation or in a report you could say the houses close to latitude 26 04 longitude 32 11 are often exposed to flooding during January and February see Figure 65 Figure 65 Graticules red lines representing the Earth s parallels of latitude and meridians of longitude The latitude and longitude values on the map border can be used for better orientation on the map A Gentle Introduction to GIS 79 8 MAP PRODUCTION Name of the map projection in detail A map projection tries to represent the 3 dimensional Earth with all its features like houses roads or lakes on a flat sheet of paper This is very difficult as you can imagine and even after hundreds of year
52. at tools can your learners use in QGIS to make sure that the new road layer is topologically correct Something to think about If you don t have a computer available you can use a map of a bus or railway network and discuss the spatial relationships and topology with your learners Further reading Books e Chang Kang Tsung 2006 Introduction to Geographic Information Systems 3rd Edition Mc Graw Hill ISBN 0070658986 A Gentle Introduction to GIS 60 GIS FOR EDUCATORS e DeMers Michael N 2005 Fundamentals of Geographic Information Systems 3rd Edition Wiley ISBN 9814126195 Websites http www innovativegis com basis primer concepts html http en wikipedia org wiki Geospatial_topology The QGIS User Guide also has more detailed information on topological editing provided in QGIS What s next In the section that follows we will take a closer look at Coordinate Reference Systems to understand how we relate data from our spherical earth onto flat maps A Gentle Introduction to GIS 61 7 COORDINATE REFERENCE SYSTEMS 7 Coordinate Reference Systems Objectives Understanding of Coordinate Ref erence Systems Keywords Coordinate Reference System CRS Map Projection On the Fly Projection Latitude Longitude Northing Easting Overview Map projections try to portray the surface of the earth or a portion of the earth on a flat piece of paper or computer screen A coordinate referen
53. ata is used to represent real world features in a GIS A vector feature can have a geometry type of point line or a polygon Each vector feature has attribute data that describes it Feature geometry is described in terms of vertices Point geometries are made up of a single vertex X Y and optionally Z Polyline geometries are made up of two or more vertices forming a connected line Polygon geometries are made up of at least four vertices forming an enclosed area The first and last vertices are always in the same place Choosing which geometry type to use depends on scale convenience and what you want to do with the data in the GIS Most GIS applications do not allow you to mix more than one geometry type in a single layer Digitising is the process of creating digital vector data by drawing it in a GIS application Vector data can have quality issues such as undershoots overshoots and slivers which you need to be aware of Vector data can be used for spatial analysis in a GIS application for example to find the nearest hospital to a school We have summarised the GIS Vector Data concept in Figure 17 A Gentle Introduction to GIS 17 2 VECTOR DATA Figure 17 This diagram shows how GIS applications deal with vector data VectorF eature red Has only one Attributes describe the Has at least two Attributes describe the Has at least four Attributes describe Vertex feature e g Lamp post Vertices fea
54. ations of reality They are designed to not only represent features but also their shape and spatial arrangement Each map projection has advantages and disadvantages The best projection for a map depends on the scale of the map and on the purposes for which it will be used For example a projection may have unacceptable distortions if used to map the entire African continent but may be an excellent choice for a large scale detailed map of your country The properties of a map projection may also influence some of the design features of the map Some A Gentle Introduction to GIS 62 GIS FOR EDUCATORS projections are good for small areas some are good for mapping areas with a large East West extent and some are better for mapping areas with a large North South extent The three families of map projections The process of creating map projections can be visualised by positioning a light source inside a transparent globe on which opaque earth features are placed Then project the feature outlines onto a two dimensional flat piece of paper Different ways of projecting can be produced by surrounding the globe in a cylindrical fashion as a cone or even as a flat surface Each of these methods produces what is called a map projection family Therefore there is a family of planar projections a family of cylindrical projections and another called conical projections see Figure 51 Figure 51 The three families of map projections They c
55. ayer Properties 7 Layer Properties General Symbology Metadata Labels Actions Attributes General Symbology Metadata Labels Actions Attributes Legend type Single Symbol 4 Transparency 0 Legend type Single Symbol Transparency 0 Label Point Symbol ongoa x AARIA PITO MODOS ds wem oe BHAS BEAR Pat t Aa LX F7AGRh eE RD DESEA LA Rotation field Area scale field Size Style Options lt off gt lt off gt 2 70 Outline style Solid Line 2 Style Options Outline color Outline style Solid Line Obie width do g Outline color dl Fill color 5 Outline width 0 26 Fill style No Brush Fill color 1 Fill style Solid Restore Default Style Save As Default Load Style Save Style Restore Default Style Save As Default Load Style Save Style ove Trn Ocoee Ore 100 cancel OK a When using simple symbols the feature is drawn b There are different options when defining simple without using an attribute to control how it looks This symbols for polyline and polygon features is the dialog for point features Graduated Symbols Sometimes vector features represent things with a changing numerical value Contour lines are a good example of this Each contour usually has an attribute value called height that contains information about what height that contour represents In Figu
56. ce system CRS then defines with the help of coordinates how the two dimensional projected map in your GIS is related to real places on the earth The decision as to which map projection and coordinate reference system to use depends on the regional extent of the area you want to work in on the analysis you want to do and often on the availability of data Map Projection in detail A traditional method of representing the earth s shape is the use of globes There is however a problem with this approach Although globes preserve the majority of the earth s shape and illustrate the spatial configuration of continent sized features they are very difficult to carry in one s pocket They are also only convenient to use at extremely small scales e g 1 100 million Most of the thematic map data commonly used in GIS applications are of considerably larger scale Typical GIS datasets have scales of 1 250 000 or greater depending on the level of detail A globe of this size would be difficult and expensive to produce and even more difficult to carry around As a result cartographers have developed a set of techniques called map projections designed to show with reasonable accuracy the spherical earth in two dimensions When viewed at close range the earth appears to be relatively flat However when viewed from space we can see that the earth is relatively spherical Maps as we will see in the upcoming map production topic are represent
57. ctor layers a_input rectangle b_input circle The resulting vector layer is displayed green Intersection Union Symetrical Difference Difference Spatial overlay is a process that allows you to identify the relationships between two polygon features that share all or part of the same area The output vector layer is a combination of the input features information see Figure 72 Typical spatial overlay examples are e Intersection The output layer contains all areas where both layers overlap intersect A Gentle Introduction to GIS 87 9 VECTOR SPATIAL ANALYSIS BUFFERS e Union the output layer contains all areas of the two input layers combined e Symmetrical difference The output layer contains all areas of the input layers except those areas where the two layers overlap intersect e Difference The output layer contains all areas of the first input layer that do not overlap inter sect with the second input layer What have we learned Let s wrap up what we covered in this worksheet e Buffer zones describe areas around real world features e Buffer zones are always vector polygons e A feature can have multiple buffer zones The size of a buffer zone is defined by a buffer distance A buffer distance has to be an integer or floating point value A buffer distance can be different for each feature within a vector layer Polygons can be buffered inward or outward from the polygon boundary Buffer zo
58. ctral resolution A Gentle Introduction to GIS 52 GIS FOR EDUCATORS If an image consists of only one band it is often called a grayscale image With grayscale images you can apply false colouring to make the differences in values in the pixels more obvious Images with false colouring applied are often referred to as pseudocolour images Raster to vector conversion In our discussion of vector data we explained that often raster data are used as a backdrop layer which is then used as a base from which vector features can be digitised Another approach is to use advanced computer programs to automatically extract vector features from images Some features such as roads show in an image as a sudden change of colour from neighbouring pixels The computer program looks for such colour changes and creates vector fea tures as a result This kind of functionality is normally only available in very specialised and often expensive GIS software Vector to raster conversion Sometimes it is useful to convert vector data into raster data One side effect of this is that attribute data that is attributes associated with the original vector data will be lost when the conversion takes place Having vectors converted to raster format can be useful though when you want to give GIS data to non GIS users With the simpler raster formats the person you give the raster image to can simply view it as an image on their computer without needing any sp
59. distinct from any other section titles You may add a section Entitled Endorsements provided it contains nothing but endorsements of your Modified Version by various parties for example statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard You may add a passage of up to five words as a Front Cover Text and a passage of up to 25 words as a Back Cover Text to the end of the list of Cover Texts in the Modified Version Only one passage of Front Cover Text and one of Back Cover Text may be added by or through arrangements made by any one entity If the Document already includes a cover text for the same cover previously added by you or by arrangement made by the same entity you are acting on behalf of you may not add another but you may replace the old one on explicit permission from the previous publisher that added the old one The author s and publisher s of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version COMBINING DOCUMENTS You may combine the Document with other documents released under this License under the terms defined in section 10 above for modified versions provided that you include in the combination all of A Gentle Introduction to GIS 103 10 SPATIAL ANALYSIS INTERPOLATION the Invariant Sections of all of the original documents unmod
60. does GIS digital data get stored Word processors spreadsheets and graphics packages are all programs that let you create and edit digital data Each type of application saves its data into a particular file format For example a graphics program will let you save your drawing as a jog JPEG image word processors let you save your document as an odt OpenDocument or doc Word Document and so on Just like these other applications GIS Applications can store their data in files on the computer hard disk There are a number of different file formats for GIS data but the most common one is probably the shape file The name is a little odd in that although we call it a shape file singular it actually consists of at least three different files that work together to store your digital vector data as shown in Table 9 Table 9 The basic files that together make up a shapefile Extension Description shp The geometry of vector features are stored in this file dbf The attributes of vector features are stored in this file shx This file is an index that helps the GIS Application to find features more quickly When you look at the files that make up a shapefile on the computer hard disk you will see something like Figure 32 If you want to share vector data stored in shapefiles with another person it is important A Gentle Introduction to GIS 34 GIS FOR EDUCATORS to give them all of
61. e is a new plugin available S 25 9980 32 1023 Scale 1 100159 E x ender E qIROOm em za A A Gentle Introduction to GIS 94 GIS FOR EDUCATORS Common problems things to be aware of It is important to remember that there is no single interpolation method that can be applied to all situations Some are more exact and useful than others but take longer to calculate They all have advantages and disadvantages In practice selection of a particular interpolation method should depend upon the sample data the type of surfaces to be generated and tolerance of estimation errors Generally a three step procedure is recommended 1 Evaluate the sample data Do this to get an idea on how data are distributed in the area as this may provide hints on which interpolation method to use 2 Apply an interpolation method which is most suitable to both the sample data and the study objectives When you are in doubt try several methods if available 3 Compare the results and find the best result and the most suitable method This may look like a time consuming process at the beginning However as you gain experience and knowledge of different interpolation methods the time required for generating the most suitable surface will be greatly reduced Other interpolation methods Although we concentrated on IDW and TIN interpolation methods in this worksheet there are more spatial interpolation methods provided in GIS s
62. ecial GIS software Raster analysis There are a great many analytical tools that can be run on raster data which cannot be used with vector data For example rasters can be used to model water flow over the land surface This information can be used to calculate where watersheds and stream networks exist based on the terrain Raster data are also often used in agriculture and forestry to manage crop production For example with a satellite image of a farmer s lands you can identify areas where the plants are growing poorly and then use that information to apply more fertilizer on the affected areas only Foresters use raster data to estimate how much timber can be harvested from an area Raster data is also very important for disaster management Analysis of Digital Elevation Models a kind of raster where each pixel contains the height above sea level can then be used to identify areas that are likely to be flooded This can then be used to target rescue and relief efforts to areas where it is needed the most A Gentle Introduction to GIS 53 5 RASTER DATA Common problems things to be aware of As we have already mentioned high resolution raster data can require large amounts of computer storage What have we learned Let s wrap up what we covered in this worksheet e Raster data are a grid of regularly sized pixels e Raster data are good for showing continually varying information e The size of pixels in a raster d
63. ent river stretches that are wide and they use river polylines to represent narrow stretches of river In Figure 33 we can see how our tourism layers might look on a map if we used all three geometry types Figure 33 A map with tourism layers We have used three different geometry types for tourism data so that we can properly represent the different kinds of features needed for our visitors giving them all the information they need 4 Quantum GIS 1 0 2 Kore 2 o x File Edit View Layer Settings Plugins Tools Help J Gd5R ROP POS ERE Pe e A 4 i Z Un O anvese QO PRD RR Legend Ex H El i ls tourism_points a Fishing r Look Out Point Xx Y tourism_lines Access Road Hiking Trail E xx 8 tourism_polys Picnic Areas x 0 50k_roads A ARTERIAL ROUTE HIKING TRAIL 1 MAIN ROAD OTHER ACCESS SECONDARY ROAD STREET TRACK FOOTPATH lx 50k_inlandwater a m g acls 2009 a S 26 0792 32 0605 scale 1 29008 x Render bry sele Elle oantosra A Gentle Introduction to GIS 36 GIS FOR EDUCATORS Example 2 Creating a map of pollution levels along a river If you wanted to measure pollution levels along the course of a river you would typically travel along the river in a boat or walk along its banks At regular intervals you would stop and take various measurements such as Dissolved Oxygen DO levels Coliform Bacteria CB counts Turbidity levels and pH
64. etermines its spatial resolution e Raster images can contain one or more bands each covering the same spatial area but con taining different information e When raster data contains bands from different parts of the electromagnetic spectrum they are called multi spectral images e Three of the bands of a multi spectral image can be shown in the colours Red Green and Blue so that we can see them e Images with a single band are called grayscale images e Single band grayscale images can be shown in pseudocolour by the GIS e Raster images can consume a large amount of storage space Now you try Here are some ideas for you to try with your learners e Discuss with your learners in which situations you would use raster data and in which you would use vector data e Get your learners to create a raster map of your school by using A4 transparency sheets with grid lines drawn on them Overlay the transparencies onto a toposheet or aerial photograph of your school Now let each learner or group of learners colour in cells that represent a certain type of feature e g building playground sports field trees footpaths etc When they are all finished overlay all the sheets together and see if it makes a good raster map representation of your school Which types of features worked well when represented as rasters How did your choice in cell size affect your ability to represent different feature types A Gentle Introduction to GI
65. far we have only created an empty shapefile Now we need to enable editing in the shapefile using the enable editing menu option or tool bar icon in the GIS Application Shapefiles are not enabled for editing by default to prevent accidentally changing or deleting the data they contain Next we need to start adding data There are two steps we need to complete for each record we add to the shapefile 1 Capturing geometry 2 Entering attributes The process of capturing geometry is different for points polylines and polygons To capture a point you first use the map pan and zoom tools to get to the correct geographical area that you are going to be recording data for Next you will need to enable the point capture tool Having done that the next place you click with the left mouse button in the map view is where you want your new point geometry to appear After you click on the map a window will appear and you can enter all of the attribute data for that point see Figure 36 If you are unsure of the data for a given field you can usually leave it blank but be aware that if you leave a lot of fields blank it will be hard to make a useful map from your data A Gentle Introduction to GIS 39 4 DATA CAPTURE Figure 36 After you have captured the point geometry you will be asked to describe its attributes The attribute form is based on the fields you specified when you created the vector layer Q Enter Attribute Values a aux
66. formity When working with a globe the main directions of the compass rose North East South and West will always occur at 90 degrees to one another In other words East will always occur at a 90 degree angle to North Maintaining correct angular properties can be preserved on a map projection as well A map projection that retains this property of angular conformity is called a conformal or orthomorphic projection These projections are used when the preservation of angular relationships is important They are commonly used for navigational or meteorological tasks It is important to remember that maintain ing true angles on a map is difficult for large areas and should be attempted only for small portions A Gentle Introduction to GIS 64 GIS FOR EDUCATORS Figure 53 The Mercator projection for example is used where angular relationships are important but the relationship of areas are distorted A b E 5 a E ATIT PCH inna of the earth The conformal type of projection results in distortions of areas meaning that if area measurements are made on the map they will be incorrect The larger the area the less accurate the area measurements will be Examples are the Mercator projection as shown in Figure ref fig mercator and the Lambert Conformal Conic projection The U S Geological Survey uses a conformal projection for many of its topographic maps Map projections with equal distance If your goal in pro
67. geometry so that you can find records in the table by selecting features on the map and find features on the map by selecting features in the table Table 4 An attribute table has fields columns and records in rows Field 1 YearBuilt Field 2 RoofColour Field 3 Balcony Record 1 1998 Red Yes Record 2 2000 Black No Record 3 2001 Silver Yes Each field in the attribute table contains contains a specific type of data text numeric or date De ciding what attributes to use for a feature requires some thought and planning In our house example earlier on in this topic we chose roof colour presence of a balcony and month of construction as attributes of interest We could just as easily have chosen other aspects of a house such as e number of levels e number of rooms e number of occupants type of dwelling RDP House block of flats shack brick house etc year the house was built e area of floor space in the house e and so on With so many options how do we make a good choice as to what attributes are needed for a feature It usually boils down to what you plan to do with the data If you want to produce a colour coded map showing houses by age it will make sense to have a Year Built attribute for your feature If you know for sure you will never use this type of map it is better to not store the information Collecting and storing unneeded information is a bad idea because of the cost
68. gt Legend JE 3 elevatlon_p1000 O x w 50k_contours 8 E gt Interpolation IDW Overview Triangulated Irregular Network TIN TIN interpolation is another popular tool in GIS A common TIN algorithm is called Delaunay trian gulation It tries to create a surface formed by triangles of nearest neighbour points To do this circumcircles around selected sample points are created and their intersections are connected to a network of non overlapping and as compact as possible triangles see Figure 77 The main disadvantage of the TIN interpolation is that the surfaces are not smooth and may give a jagged appearance This is caused by discontinuous slopes at the triangle edges and sample data points In addition triangulation is generally not suitable for extrapolation beyond the area with collected sample data points see Figure 78 A Gentle Introduction to GIS 93 10 SPATIAL ANALYSIS INTERPOLATION Figure 77 Delaunay triangulation with circumcircles around the red sample data The resulting interpolated TIN surface created from elevation vector points is shown on the right Image Source Mitas L Mitasova H 1999 File Edit View Layer Settings Plugins Tools Help dadde PPS ORARAA O e Tao RR FONMNEPOLO SY Lae rr MReoOaN gt lt gt DO gt U gt ay a gt gt E X s rainfall_january mm degrees o B DRS 50k_contours 68 E e Y Interpolation QGIS 2009 Ther
69. he attribute table lower image lists the attributes for the house areas shown on the map When a feature is highlighted in the table it will appear as a yellow polygon on the map i 4 Quantum GIS 1 0 2 Kore EasternCapeVectors Layer Plugins Tools Tools Help a RARRARPLPO BREBO 209 gt oORARAALO YR RRSORR File Edit View fa Beet ea Legend ae Black M Red vI Building Points vi Trees YE Roads amp Road Outlines v 8 Water Bodies VIK Rivers vi Spot Height y aor Y Y Contours y Building Areas vI River Areas E 4 0 1 0 4 B E E 0 E al Bia 4 2000 1 2008 1 2001 0 2004 1 0 Red 2 1 Black 3 2 Red 4 3 Black 4 Qo a212 1 8r 01384 01104 There is a new plugin available 26 0722 32 0766 Scale 1 31810 69 vi Render isp Attribute table houses id RoofColour HasBalcony DateBuilt tela zD Mu gt 0 0 01 TT degrees 1247 LES Cial a y Search for in RoofColour zll Search select El Advanced l Herp Lose A Gentle Introduction to GIS 22 GIS FOR EDUCATORS The fact that features have attributes as well geometry in a GIS Application opens up many possibili ties For example we can use the attribute values to tell the GIS what colours and style to use when drawing features see Figure 22 The process of setting colours and drawing styles is often
70. he point polyline or polygon capture tool active and start to draw your next feature When you have no more features to add always be sure to click the allow editing icon to toggle it off The GIS Application will then save your newly created layer to the hard disk A Gentle Introduction to GIS 40 GIS FOR EDUCATORS Figure 37 Capturing lines for a tourism map When editing a line layer the vertices are shown with circular markers which you can move about with the mouse to adjust the line s geometry When adding a new line shown in red each click of the mouse will add a new vertex G Quantum GIS 1 0 2 Kore E j ioj xj File Edit view Layer Settings Plugins Tools Help Jada 5 RRO PPE URE gt ree 7 Da09AF xu0 vad QQ Legend IES ro El 24 tourism_points 21 Woegree Fishing fr Look Out Point tourism_lines Access Road Hiking Trail e tourism_polys Picnic Areas E 9 50k_roads ARTERIAL ROUTE HIKING TRAIL 1 MAIN ROAD OTHER ACCESS SECONDARY ROAD STREET TRACK FOOTPATH X 50k_inlandwater a fon ISA Heads up digitising As you have probably discovered by now if you followed the steps above it is pretty hard to draw the features so that they are spatially correct if you do not have other features that you can use as a point of reference One common solution to this problem is to use a raster layer such as an aerial photograph or a satellite image a
71. ics a Secondary Section may not explain any mathematics The relationship could be a matter of historical connection with the subject or with related matters or of legal commercial philosophical ethical or political position regarding them The Invariant Sections are certain Secondary Sections whose titles are designated as being those of Invariant Sections in the notice that says that the Document is released under this License If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant The Document may contain zero Invariant Sections If the Document does not identify any Invariant Sections then there are none The Cover Texts are certain short passages of text that are listed as Front Cover Texts or Back Cover Texts in the notice that says that the Document is released under this License A Front Cover Text may be at most 5 words and a Back Cover Text may be at most 25 words A Transparent copy of the Document means a machine readable copy represented in a format whose specification is available to the general public that is suitable for revising the document straightforwardly with generic text editors or for images composed of pixels generic paint programs or for drawings some widely available drawing editor and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters A copy made
72. ieee Dp ert TT E Unknown value 2 dl i s _ to be interpolated 4 e i Si i i Weighting is assigned to sample points through the use of a weighting coefficient that controls how the weighting influence will drop off as the distance from new point increases The greater the weighting coefficient the less the effect points will have if they are far from the unknown point during the interpolation process As the coefficient increases the value of the unknown point approaches the A Gentle Introduction to GIS 92 GIS FOR EDUCATORS value of the nearest observational point It is important to notice that the IDW interpolation method also has some disadvantages The quality of the interpolation result can decrease if the distribution of sample data points is uneven Fur thermore maximum and minimum values in the interpolated surface can only occur at sample data points This often results in small peaks and pits around the sample data points as shown in Figure 75 In GIS interpolation results are usually shown as a 2 dimensional raster layer In Figure 76 you can see a typical IDW interpolation result based on elevation sample points collected in the field with a GPS device Figure 76 IDW interpolation result from irregularly collected elevation sample points shown as black crosses A ESOO ROre project dk View Layer Settings Plugins Tools Help agaceererere MRZIO 2B eSOPRR FONE 0OL0OS Da EOLADIAR QO V WMATA
73. ified and list them all as Invariant Sec tions of your combined work in its license notice and that you preserve all their Warranty Disclaimers The combined work need only contain one copy of this License and multiple identical Invariant Sec tions may be replaced with a single copy If there are multiple Invariant Sections with the same name but different contents make the title of each such section unique by adding at the end of it in paren theses the name of the original author or publisher of that section if known or else a unique number Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work In the combination you must combine any sections Entitled History in the various original docu ments forming one section Entitled History likewise combine any sections Entitled Acknowledge ments and any sections Entitled Dedications You must delete all sections Entitled Endorse ments COLLECTIONS OF DOCUMENTS You may make a collection consisting of the Document and other documents released under this License and replace the individual copies of this License in the various documents with a single copy that is included in the collection provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects You may extract a single document from such a collection and distribute it individually
74. ify Add class Delete classes Randomize Colors Reset Colors 1 ARTERIAL ROUTE HIKING TRAIL MAIN ROAD N OTHER ACCESS Label SECONDARY ROAD STREET TRACK FOOTPATH Style Options Outline style Outline color Outline width Fill color Fill style Restore Default Style Save As Default Load Style Save Style Help P Apply OQ Cancel ok J When the GIS draws the layer it will look at the attributes of each feature before drawing it to the screen Based on the value in the chosen field in the attribute table the road line will be drawn with suitable colour and line style and fill style if its a polygon feature This is shown in Figure 31 A Gentle Introduction to GIS 30 GIS FOR EDUCATORS Figure 31 A roads vector layer symbolised using a unique value per road type Things to be aware of Deciding which attributes and symbology to use requires some planning Before you start collecting any GeoSpatial data you should ensure you know what attributes are needed and how it will be symbolised It is very difficult to go back and re collect data if you plan poorly the first time around Remember also that the goal of collecting attribute data is to allow you to analyse and interpret spatial information How you do this depends on the questions you are trying to answer Symbology is a visual language that allows people to see and understand your attribute data based on the colours and symbols you use Because of this
75. ilable you can show your pupils the principles of the three map projection families Get a globe and paper and demonstrate how cylindrical conical and planar projections work in general With the help of a transparency sheet you can draw a two dimensional coordinate reference system showing X axes and Y axes Then let your pupils define coordinates x and y values for different places Further reading Books A Gentle Introduction to GIS 73 7 COORDINATE REFERENCE SYSTEMS e Chang Kang Tsung 2006 Introduction to Geographic Information Systems 3rd Edition Mc Graw Hill ISBN 0070658986 e DeMers Michael N 2005 Fundamentals of Geographic Information Systems 3rd Edition Wiley ISBN 9814126195 e Galati Stephen R 2006 Geographic Information Systems Demystified Artech House Inc ISBN 158053533X Websites http www colorado edu geography gcraft notes mapproj mapproj_f html http geology isu edu geostac Field_Exercise topomaps index htm The QGIS User Guide also has more detailed information on working with map projections in QGIS What s next In the section that follows we will take a closer look at Map Production A Gentle Introduction to GIS 74 GIS FOR EDUCATORS 8 Map Production Objectives Understanding of map production for spatial data Keywords Map production map layout scale bar north arrow legend map body map unit Overview Map production is the process
76. into 60 equal zones that are all 6 degrees wide in longitude from East to West The UTM zones are numbered 1 to 60 starting at the international date line zone 1 at 180 degrees West longitude and progressing East back to the international date line zone 60 at 180 degrees East longitude as shown in Figure 59 Figure 59 The Universal Transverse Mercator zones For South Africa UTM zones 33S 34S 35S and 36S are used As you can see in Figure 59 and Figure 60 South Africa is covered by four UTM zones to minimize distortion The zones are called UTM 33S UTM 34S UTM 35S and UTM 36S The S after the zone means that the UTM zones are located south of the equator Say for example that we want to define a two dimensional coordinate within the Area of Interest AOI marked with a red cross in Figure 60 You can see that the area is located within the UTM zone 35S This means to minimize distortion and to get accurate analysis results we should use UTM zone 35S as the coordinate reference system The position of a coordinate in UTM south of the equator must be indicated with the zone number A Gentle Introduction to GIS 70 GIS FOR EDUCATORS Figure 60 UTM zones 33S 34S 35S and 36S with their central longitudes meridians used to project South Africa with high accuracy The red cross shows an Area of Interest AOI I I I EF EF ae EIF as ae Ti BID Hj O Hj O 10 o a Qi Qi JE Fi amp EE Se 1 1
77. ints represent trees c After making our adjustments it is much easier to A Gentle Introduction to GIS 15 2 VECTOR DATA What can we do with vector data in a GIS At the simplest level we can use vector data in a GIS Application in much the same way you would use a normal topographic map The real power of GIS starts to show itself when you start to ask questions like which houses are within the 100 year flood level of a river where is the best place to put a hospital so that it is easily accessible to as many people as possible which learners live in a particular suburb A GIS is a great tool for answering these types of questions with the help of vector data Generally we refer to the process of answering these types of questions as spatial analysis In later topics of this tutorial we will look at spatial analysis in more detail Common problems with vector data Working with vector data does have some problems We already mentioned the issues that can arise with vectors captured at different scales Vector data also needs a lot of work and maintenance to ensure that it is accurate and reliable Inaccurate vector data can occur when the instruments used to capture the data are not properly set up when the people capturing the data aren t being careful when time or money don t allow for enough detail in the collection process and so on If you have poor quality vector data you can often detect this when vie
78. is mean to the map reader It means that if you multiply the distance measured on the map by the scale denominator you will know the distance in the real world For example if we want to measure a distance of 100mm on a map with a scale of 1 25 000 we calculate the real world distance like this 100mm x 25 000 2 500 000 mm This means that 100mm on the map is equivalent to 2 500 000mm 250m in the real word Figure 64 Maps showing an area in two different scales The map scale on the left is 1 25 000 The map scale on the right is 1 50 000 gt 08 Sy la J pS Another interesting aspect of a map scale is that the lower the map scale the more detailed the feature information in the map will be In Figure 64 you can see an example of this Both maps are the same size but have a different scale The image on the left side shows more details for example the houses south west of the water body can be clearly identified as separate squares In the image A Gentle Introduction to GIS 78 GIS FOR EDUCATORS on the right you can only see a black clump of rectangles and you are not able to see each house clearly Acknowledgment in detail In the acknowledgment area of a map it is possible to add text with important information For example information about the quality of the used data can be useful to give the reader an idea about details such as how by whom and when a map was created If you look
79. ited resources data collection is usually conducted only in a limited number of selected point locations In GIS spatial interpolation of these points can be applied to create a raster surface with estimates made for all raster cells In order to generate a continuous map for example a digital elevation map from elevation points measured with a GPS device a suitable interpolation method has to be used to optimally estimate the values at those locations where no samples or measurements were taken The results of the interpolation analysis can then be used for analyses that cover the whole area and for modelling There are many interpolation methods In this introduction we will present two widely used interpola tion methods called Inverse Distance Weighting IDW and Triangulated Irregular Networks TIN If you are looking for additional interpolation methods please refer to the further reading section at the end of this topic Inverse Distance Weighted IDW In the IDW interpolation method the sample points are weighted during interpolation such that the influence of one point relative to another declines with distance from the unknown point you want to create see Figure 75 Figure 75 Inverse Distance Weighted interpolation based on weighted sample point distance left Interpo lated IDW surface from elevation vector points right Image Source Mitas L Mitasova H 1999 Sample Points gt i Sample Points a X j
80. jecting a map is to accurately measure distances you should select a projection that is designed to preserve distances well Such projections called equidistant projections require that the scale of the map is kept constant A map is equidistant when it correctly represents distances from the centre of the projection to any other place on the map Equidistant projections maintain accurate distances from the centre of the projection or along given lines These projections are used for radio and seismic mapping and for navigation The Plate Carree Equidistant Cylindrical see Figure 55 and the Equirectangular projection are two good examples of equidistant projections The Azimuthal Equidistant projection is the projection used for the emblem of the United Nations see Figure 54 A Gentle Introduction to GIS 65 7 COORDINATE REFERENCE SYSTEMS Figure 54 The United Nations Logo uses the Azimuthal Equidistant projection Figure 55 The Plate Carree Equidistant Cylindrical projection for example is used when accurate distance measurement is important Projections with equal areas When a map portrays areas over the entire map so that all mapped areas have the same proportional
81. layers do not usually have any attribute data associated with them A Gentle Introduction to GIS 50 GIS FOR EDUCATORS Spatial Resolution Every raster layer in a GIS has pixels cells of a fixed size that determine its spatial resolution This becomes apparent when you look at an image at a small scale see Illustration 5 below and then zoom in to a large scale see Illustration 6 below Figure 45 This satellite image looks good when using a small scale Figure 46 but when viewed at a large scale you can see the individual pixels that the image is composed of Several factors determine the spatial resolution of an image For remote sensing data spatial res olution is usually determined by the capabilities of the sensor used to take an image For example SPOT5 satellites can take images where each pixel is 10m x 10m Other satellites for example MODIS take images only at 500m x 500m per pixel In aerial photography pixel sizes of 50cm x 50cm are not uncommon Images with a pixel size covering a small area are called high resolu tion images because it is possible to make out a high degree of detail in the image Images with a pixel size covering a large area are called low resolution images because the amount of detail the A Gentle Introduction to GIS 51 5 RASTER DATA images show is low In raster data that is computed by spatial analysis such as the rainfall map we mentioned earlier the spati
82. le in Figure a below Another option is the representative fraction RF method where both the map distance and the ground distance in the real world are given in the same map units as a ratio For example a RF value 1 25 000 means that any distance on the map is 1 25 000th of the real distance on the ground see Figure 63b below The value 25 000 in the ratio is called the scale denominator More experienced users often prefer the representative fraction method because it reduces confusion When a representative fraction expresses a very small ratio for example 1 1000 000 it is called a small scale map On the other hand if the ratio is very large for example a 1 50 000 map it is called a large scale map It is handy to remember that a small scale map covers a large area and a large scale map covers a small area A scale expression as a graphic or bar scale is another basic method of expressing a scale A bar scale shows measured distances on the map The equivalent distance in the real world is placed A Gentle Introduction to GIS 77 8 MAP PRODUCTION above as you can see in Figure 63c below Figure 63 A map scale can be expressed in words a as a ratio b or as graphic or bar scale c a 1 centimeter represents 250 meters 1 25 000 E 1000 2000 3000 4000 meters R A E Maps are usually produced at standard scales of for example 1 10 000 1 25 000 1 50 000 1 100 000 1 250 000 1 500 000 What does th
83. lour symbology is defined and looks The process starts by setting the layers properties to continuous colour using a dialog like the one shown in Figure 28 A Gentle Introduction to GIS 2 00 GIS FOR EDUCATORS Figure 28 Setting up continuous colour symbology The contour height attribute is used to determine colour values Colours are defined for the minimum and maximum values The GIS Application will then create a gradient of colours for drawing the features based on their heights rayer Properties x General Symbology Metadata Labels Actions Attributes Legend type Continuous Color Transparency 0 Classification Field HEIGHT 4 Minimum Value E Maximum Value Outline Width 0 26 E Restore Default Style J Save As Default at Load Style m IL Save Style el O Help 2 Apply Cancel gi OK After defining the minimum and maximum colours in the colour range the colour features are drawn in will depend on where the attribute lies in the range between minimum and maximum For example if you have contour features with values starting at 1000m and ending at 1400m the value range is 1000 to 1400 If the colour set for the minimum value is set to orange and the colour for the maximum value is black contours with a value of close to 1400m will be drawn close to black On the other hand contours with a value near to 1000m will be drawn close to orange see Figure 29 Figure
84. lved left and with intact boundaries right showing overlapping areas A Gentle Introduction to GIS 86 GIS FOR EDUCATORS Buffering outward and inward Buffer zones around polygon features are usually extended outward from a polygon boundary but it is also possible to create a buffer zone inward from a polygon boundary Say for example the Department of Tourism wants to plan a new road around Robben Island and environmental laws require that the road is at least 200 meters inward from the coast line They could use an inward buffer to find the 200m line inland and then plan their road not to go beyond that line Common problems things to be aware of Most GIS Applications offer buffer creation as an analysis tool but the options for creating buffers can vary For example not all GIS Applications allow you to buffer on either the left side or the right side of a line feature to dissolve the boundaries of buffer zones or to buffer inward from a polygon boundary A buffer distance always has to be defined as a whole number integer or a decimal number floating point value This value is defined in map units meters feet decimal degrees according to the Coordinate Reference System CRS of the vector layer More spatial analysis tools Buffering is a an important and often used spatial analysis tool but there are many others that can be used in a GIS and explored by the user Figure 72 Spatial overlay with two input ve
85. make out any individual features from the image Spectral resolution If you take a colour photograph with a digital camera or camera on a cellphone the camera uses electronic sensors to detect red green and blue light When the picture is displayed on a screen or printed out the red green and blue RGB information is combined to show you an image that your eyes can interpret While the information is still in digital format though this RGB information is stored in separate colour bands Whilst our eyes can only see RGB wavelengths the electronic sensors in cameras are able to detect wavelengths that our eyes cannot Of course in a hand held camera it probably doesn t make sense to record information from the non visible parts of the spectrum since most people just want to look at pictures of their dog or what have you Raster images that include data for non visible parts of the light spectrum are often referred to as multi spectral images In GIS recording the non visible parts of the spectrum can be very useful For example measuring infra red light can be useful in identifying water bodies Because having images containing multiple bands of light is so useful in GIS raster data are often provided as multi band images Each band in the image is like a separate layer The GIS will combine three of the bands and show them as red green and blue so that the human eye can see them The number of bands in a raster image is referred to as its spe
86. mmon types of buffer zones may be greenbelts between residential and commercial areas border zones between countries see Figure 67 noise protection zones around airports or pollution protection zones along rivers A Gentle Introduction to GIS 83 9 VECTOR SPATIAL ANALYSIS BUFFERS Figure 67 The border between the United States of America and Mexico is separated by a buffer zone Photo taken by SGT Jim Greenhill 2006 In a GIS Application buffer zones are always represented as vector polygons enclosing other polygon line or point features see Figures 68a c Figure 68 Buffering vector points polylines and polygons a A buffer zone around vector b A buffer zone around vector poly c A buffer zone around vector poly points lines gons Variations in buffering There are several variations in buffering The buffer distance or buffer size can vary according to numerical values provided in the vector layer attribute table for each feature The numerical values A Gentle Introduction to GIS 84 GIS FOR EDUCATORS have to be defined in map units according to the Coordinate Reference System CRS used with the data For example the width of a buffer zone along the banks of a river can vary depending on the intensity of the adjacent land use For intensive cultivation the buffer distance may be bigger than for organic farming see Figure 69 and Table 11 Figure 69 Buffering rivers with different buffer dista
87. nce org curriculum waterproj SO0project miami2000 miamiriverfinal html A school project to assess water quality in their local river The QGIS User Guide also has more detailed information on digitising vector data in QGIS What s next In the section that follows we will take a closer look at raster data to learn all about how image data can be used in a GIS A Gentle Introduction to GIS 46 GIS FOR EDUCATORS 5 Raster Data Objectives Understanding what raster data is and how it can be used in a GIS Keywords Raster Pixels Remote Sensing Satellite Image Georeference Overview In the previous topics we have taken a closer look at vector data While vector features use geometry points polylines and polygons to represent the real world raster data takes a different approach Rasters are made up of a matrix of pixels also called cells each containing a value that represents the conditions for the area covered by that cell see Figure 41 In this topic we are going to take a closer look at raster data when it is useful and when it makes more sense to use vector data Figure 41 A raster dataset is composed of rows running across and columns running down of pixels also know as cells Each pixel represents a geographical region and the value in that pixel represents some characteristic of that region Raster PL iol Poh A Wn Oo a fees Columns i A Gentle Introduction to GIS 47 5 R
88. nces Table 11 Attribute table with different buffer distances to rivers based on information about the adjacent land use River Adjacent land use Buffer distance meters Breede river Intensive vegetable cultivation 100 Komati Intensive cotton cultivation 150 Oranje Organic farming 50 Telle river Organic farming 50 Buffers around polyline features such as rivers or roads do not have to be on both sides of the lines They can be on either the left side or the right side of the line feature In these cases the left or right side is determined by the direction from the starting point to the end point of line during digitising Multiple buffer zones A feature can also have more than one buffer zone A nuclear power plant may be buffered with dis tances of 10 15 25 and 30 km thus forming multiple rings around the plant as part of an evacuation plan see Figure 70 A Gentle Introduction to GIS 85 9 VECTOR SPATIAL ANALYSIS BUFFERS Figure 70 Buffering a point feature with distances of 10 15 25 and 30 km Buffering with intact or dissolved boundaries Buffer zones often have dissolved boundaries so that there are no overlapping areas between the buffer zones In some cases though it may also be useful for boundaries of buffer zones to remain intact so that each buffer zone is a separate polygon and you can identify the overlapping areas see Figure 71 Figure 71 Buffer zones with disso
89. nd cie 76 Map Border IAS oo ia AA A ee A 76 Map Legend ATA lt ec s co w caa EA SAA A RE A oe 76 NT arrow immdetail ono reaa e A WR eee eed amp a OR a ae es 77 Scale ac es AE o A ee EI eee Pe NS 77 Acknowledgment in detail ooa 24 79 A 79 A Gentle Introduction to GIS vi GIS FOR EDUCATORS Name of the map projection in detail o o eee eee ee 80 Common problems things to be aware of oaao a ee 80 What have we learned ooco A Re ea 81 FIRES ona vee ee oat ee se AER ee BS ee Be BOR ATS 81 Something to think about lt cece See eee ar RA 81 Farner reading 2 3 4 6 44 a dar A a KRE oar A A a red aa A e a 81 WIA S NEX pada ingi as CAS a ee OO as E A A 82 9 Vector Spatial Analysis Buffers 83 COMINO isidro ARA A EOS AM LOS H 83 B itermg MAAA gt ere da dai aea A e tl ia 83 Variations in buffering RR 84 Mu ltiple buffer ZONES os ov ada a A SEE e eS 85 Buffering with intact or dissolved boundaries o e e aes 86 Buffering outward and inward lt lt 2 As A A e 87 Common problems things to be aware of o o 87 More spatial analysis tools e e 87 What have we learned ee ee 88 NOW VOOY iia ii i 5 4 8 4GR PRES aae d SS fa iee die SE 4B EGRESS Ge Ee GS 88 Something to think about 2 6 d bed a See Dade ee See Poe eRe a ee 89 Further reading o c s cos 640 Ewha Pa ra yok Skeet eh ad 89
90. nd to use the data you capture at a scale of 1 50 000 later What have we learned Let s wrap up what we covered in this worksheet e Digitising is the process of capturing knowledge of a feature s geometry and attributes into a digital format stored on the computer s disk e GIS Data can be stored in a database or as files e One commonly used file format is the shapefile which is actually a group of three or more files shp dbf and shx A Gentle Introduction to GIS 44 GIS FOR EDUCATORS e Before you create a new vector layer you need to plan both what geometry type and attribute fields it will contain e Geometry can be point polyline or polygon e Attributes can be integers whole numbers floating points decimal numbers strings words or dates e The digitising process consists of drawing the geometry in the map view and then entering its attributes This is repeated for each feature e Heads up digitising is often used to provide orientation during digitising by using a raster image in the background e Professional GIS users sometimes use a digitising table to capture information from paper maps Now you try Here are some ideas for you to try with your learners e Draw up a list of features in and around your school that you think would be interesting to capture For example the school boundary the position of fire assembly points the layout of each class room and so on Try to use a mix of diffe
91. nes can be created with intact or dissolved boundaries Besides buffering a GIS usually provides a variety of vector analysis tools to solve spatial tasks Now you try e Because of dramatic traffic increase the town planners want to widen the main road and add a second lane Create a buffer around the road to find properties that fall within the buffer zone see Figure 73 e For controlling protesting groups the police want to establish a neutral zone to keep protesters at least 100 meters from a building Create a buffer around a building and colour it so that event planners can see where the buffer area is e A truck factory plans to expand The siting criteria stipulate that a potential site must be within 1 km of a heavy duty road Create a buffer along a main road so that you can see where potential sites are e Imagine that the city wants to introduce a law stipulating that no bottle stores may be within a 1000 meter buffer zone of a school or a church Create a 1km buffer around your school and then go and see if there would be any bottle stores too close to your school A Gentle Introduction to GIS 88 GIS FOR EDUCATORS Figure 73 Buffer zone green around a roads map brown You can see which houses fall within the buffer zone so now you could contact the owner and talk to him about the situation HOUSE Something to think about If you don t have a computer available you can use a toposheet and a compass to
92. ngly important tool in environmental management retail military police tourism and many other spheres of our daily lives If you use a computer or a cell phone you have probably already used a GIS in some form without even realising it Maybe it was a map on a web site Google Earth an information booth or your cell phone telling you where you are Proprietary GIS software software that cannot be freely shared or modified is available that will let you do everything we describe in these worksheets and a lot more However this software is usually very expensive or otherwise limits your freedom to copy share and modify the software GIS vendors sometimes make an exception for educational activities providing cheaper or free copies of their software They do this knowing that if teachers and learners get to know their software they will be reluctant to learn other packages When learners leave school they will go into the workplace and buy the commercial software never knowing that there are free alternatives that they could be using With Quantum GIS we offer an alternative software that is free of cost and free in a social sense You can make as many copies as you like When learners leave school one day they can use this software to build their skills solve problems at work and make the world a better place When you buy commercial software you limit your options for the future By learning using and sharing Free and Open Source Software
93. nly used functions Holding your mouse over a picture will usually tell you what will happen when you click on it Jadore aeea YS TESSRR ONBHM OOS TKK Meio NA eu AG YIOLAO0NAFAR Ro PHAPQQIQVego A common function of GIS Applications is to display map layers Map layers are stored as files on a disk or as records in a database Normally each map layer will represent something in the real world a roads layer for example will have data about the street network When you open a layer in the GIS Application it will appear in the map view The map view shows A Gentle Introduction to GIS 3 1 INTRODUCING GIS a graphic representing your layer When you add more than one layer to a map view the layers are overlaid on top of each other Figure 4 below shows a map view that has several layers being added to it An important function of the map view is to allow you to zoom in to magnify zoom out to see a greater area and move around panning in the map Figure 4 A map view with several layers being added to it 0 0 01 0 0 01 1 degrees 1 degrees Ea Queenst g Queensto own ga A wn E N y o O QGIS 2009 E QGIS 2009 a A towns layer added to the map view b A schools layer added to the map view 0 0 01 0 0 01 MM degrees E M degrees 2 a po or E a See E a AL ATA a Neg To pa hn thy 2 s amp by y 0 2 ony 2 Es o aaisa E o aci
94. nside the computer s memory Vector data is used to represent points lines and areas Figure 7 shows different types of vector data being viewed in a GIS application In the tutorials that follow we will be exploring vector data in more detail Figure 7 Vector data is used to represent points e g towns lines e g rivers and polygons e g municipal boundaries an Koffica So SL Baais 2009 A Gentle Introduction to GIS 6 GIS FOR EDUCATORS Raster data are stored as a grid of values There are many satellites circling the earth and the photographs they take are a kind of raster data that can be viewed in a GIS One important difference between raster and vector data is that if you zoom in too much on a raster image it will start to appear blocky see Figure 8 In fact these blocks are the individual cells of the data grid that makes up the raster image We will be looking at raster data in greater detail in later tutorials Figure 8 Zoom in to see the individual cells of the data grid that makes up the raster image a Raster data are often images taken by satellites b The same raster data but this time zoomed in The Here we can see mountains in the Eastern Cape grid nature of the data can be seen What have we learned Let s wrap up what we covered in this worksheet e AGIS is a system of computer hardware computer software and geographical data e A GIS Application allows you to view geogra
95. of arranging map elements on a sheet of paper in a way that even without many words the average person can understand what it is all about Maps are usually pro duced for presentations and reports where the audience or reader is a politician citizen or a learner with no professional background in GIS Because of this a map has to be effective in communicating spatial information Common elements of a map are the title map body legend north arrow scale bar acknowledgement and map border see Figure 61 Figure 61 Common map elements labelled in red are the title map body legend north arrow scale bar acknowledgement and map border Title Common map elements 0 01 degree Scale bar North arrow Legend Buildings s Contour lines Lakes Sa Rivers Roads Other Access Track Footpath Spotheigts Data Source GIS for Educators A Gentle Introduction to GIS 75 8 MAP PRODUCTION Other elements that might be added are e g a graticule or name of the map projection CRS Together these elements help the map reader to interpret the information shown on the map The map body is of course the most important part of the map because it contains the map information The other elements support the communication process and help the map reader to orientate himself and understand the map topic For example the title describes the subject matter and the legend relates map symbols to the mapped data Map Ti
96. ols to show the popularity of each footpath Places where taps are Point Single Symbol located Classrooms Polygon Unique Value based on the grade of the learners in the classroom Fence Polyline Have your learners rate the condition of the fence around your school by separating it into sections and grading each section on a scale of 1 9 based on its condition Use graduated symbols to classify the condition attribute Classrooms Polygon Count the number of learners in each classroom and use a continuous colour symbol to define a range of colours from red to blue What s next In the section that follows we will take a closer look at data capture We will put the things we have learned about vector data and attributes into practice by creating new data A Gentle Introduction to GIS 33 4 DATA CAPTURE 4 Data Capture Objectives Learn how to create and edit vector and attribute data Keywords Editing data capture heads up ta ble database Overview In the previous two topics we looked at vector data We saw that there are two key concepts to vector data namely geometry and attributes The geometry of a vector feature describes its shape and position while the attributes of a vector feature describe its properties colour size age etc In this section we will look more closely at the process of creating and editing vector data both the geometry and attributes of vector features How
97. olylines are digitised captured into the computer with distances between vertices that are small enough for the scale at which you want to use the data The attributes of a polyline decribe its properties or characteristics For example a road polyline may have attributes that describe whether it is surfaced with gravel or tar how many lanes it has whether it is a one way street and so on The GIS can use these attributes to symbolise the polyline feature with a suitable colour or line style Figure 12 Polylines viewed at a smaller scale 1 20 000 to the left may appear smooth and curved When zoomed in to a larger scale 1 500 to the right polylines may look very angular y s 1262 O QGIS 2009 QGIS 2009 Polygon features in detail Polygon features are enclosed areas like dams islands country boundaries and so on Like polyline features polygons are created from a series of vertices that are connected with a continuous line However because a polygon always describes an enclosed area the first and last vertices should al ways be at the same place Polygons often have shared geometry boundaries that are in common with a neighbouring polygon Many GIS applications have the capability to ensure that the bound aries of neighbouring polygons exactly coincide We will explore this in the topology topic later in A Gentle Introduction to GIS 12 GIS FOR EDUCATORS this tutorial As with points and polylines polygons ha
98. ommonly used projections and when data is exchanged people will follow the national trend Figure 56 The Mollweide Equal Area Cylindrical projection for example ensures that all mapped areas have the same proportional relationship to the areas on the Earth ARS gt A ROA g P P Sew ILLERA A PEREA AA EXQUUA AT WS Wa JEF Coordinate Reference System CRS in detail With the help of coordinate reference systems CRS every place on the earth can be specified by a set of three numbers called coordinates In general CRS can be divided into projected coordi nate reference systems also called Cartesian or rectangular coordinate reference systems and geographic coordinate reference systems Geographic Coordinate Systems The use of Geographic Coordinate Reference Systems is very common They use degrees of latitude and longitude and sometimes also a height value to describe a location on the earth s surface The most popular is called WGS 84 Lines of latitude run parallel to the equator and divide the earth into 180 equally spaced sections A Gentle Introduction to GIS 67 7 COORDINATE REFERENCE SYSTEMS from North to South or South to North The reference line for latitude is the equator and each hemisphere is divided into ninety sections each representing one degree of latitude In the northern hemisphere degrees of lati
99. on scale let s look at cities for example If you have a small scale map which covers a large area it may make sense to represent a city using a point feature However as you zoom in to the map moving towards a larger scale it makes more sense to show the city limits as a polygon When you choose to use points to represent a feature is mostly a matter of scale how far away are you from the feature convenience it takes less time and effort to create point features than polygon features and the type of feature some things like telephone poles just don t make sense to be stored A Gentle Introduction to GIS 10 GIS FOR EDUCATORS as polygons Figure 11 Landscape features as we would present them in a GIS Rivers blue and roads green can be represented as lines trees as points red and houses as polygons white As we show in Illustration 2 a point feature has an X Y and optionally Z value The X and Y values will depend on the Coordinate Reference System CRS being used We are going to go into more detail about Coordinate Reference Systems in a later tutorial For now let s simply say that a CRS is a way to accurately describe where a particular place is on the earth s surface One of the most common reference systems is Longitude and Latitude Lines of Longitude run from the North Pole to the South Pole Lines of Latitude run from the East to West You can describe precisely where you are at any place on the ea
100. ona c A railways layer added to the map view d A rivers layer added to the map view Unlike paper maps the maps displayed in GIS Applications can be changed after they have been created You can change the symbology of the map layers to make them appear in different colours or symbols For example if we take the map in Figure 4 d and change the symbology we can completely change how it looks as shown in Figure 5 Symbology plays an important role in how we interpret maps and GIS Applications are very good at letting you change symbology quickly and easily Another common feature of GIS Applications is the map legend The map legend provides a list of layers that have been loaded in the GIS Application Unlike a paper map legend the map legend or layers list in the GIS Application provides a way to re order hide show and group layers Changing the layer order is done by clicking on a layer in the legend holding the mouse button down and then dragging the layer to a new position In Figure 6 the map legend is shown as the area to the left of the GIS Application window By changing the layer order the way that layers are drawn can be adjusted in this case so that rivers are drawn over the roads instead of below them A Gentle Introduction to GIS 4 GIS FOR EDUCATORS Figure 5 GIS Software let you easily change symbology the way information is displayed 0 0 01 m degrees A E ee dy Cueenstown e e
101. opy if you have access to the internet A Gentle Introduction to GIS 1 INTRODUCING GIS GIS Data Now that we know what a GIS is and what a GIS Application can do let s talk about GIS data Data is another word for information The information we use in a GIS normally has a geographical aspect to it Think of our example above about the health care worker She created a table to record diseases that looked like this Table 2 Example from table 1 with date and place of residence of patients Longitude Latitude Disease Date 26 870436 31 909519 Mumps 13 12 2008 The longitude and latitude columns hold geographical data The disease and date columns hold non geographical data A common feature of GIS is that they allow you to associate information non geographical data with places geographical data In fact the GIS Application can store many pieces of information which are associated with each place something that paper maps are not very good at For example our health care worker could store the person s age and gender on her table When the GIS Application draws the layer you can tell it to draw the layer based on gender or based on disease type and so on So with a GIS Application we have a way to easily change the appearance of the maps we created based on the non geographical data associated with places GIS Systems work with many different types of data Vector data is stored as a series of X Y coordinate pairs i
102. or entities responsible for authorship of the modifications in the Modified Version together with at least five of the principal authors of the Document all of its principal authors if it has fewer than five unless they release you from this requirement 3 State on the Title page the name of the publisher of the Modified Version as the publisher 4 Preserve all the copyright notices of the Document 5 Add an appropriate copyright notice for your modifications adjacent to the other copyright no tices 6 Include immediately after the copyright notices a license notice giving the public permission to use the Modified Version under the terms of this License in the form shown in the Addendum below 7 Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document s license notice 8 Include an unaltered copy of this License 9 Preserve the section Entitled History Preserve its Title and add to it an item stating at least the title year new authors and publisher of the Modified Version as given on the Title Page If there is no section Entitled History in the Document create one stating the title year authors and publisher of the Document as given on its Title Page then add an item describing the Modified Version as stated in the previous sentence A Gentle Introduction to GIS 102 GIS FOR EDUCATORS 10 Preserve the network location if any given
103. ork analysis e g finding the best route across a road network or measurement e g finding out the length of a river In addition to topology being useful for network analysis and measurement there are other reasons why it is important and useful to create or have vector data with correct topology Just imagine you digitise a municipal boundaries map for your province and the polygons overlap or show slivers If such errors were present you would be able to use the measurement tools but the results you get will be incorrect You will not know the correct area for any municipality and you will not be able to define exactly where the borders between the municipalities are It is not only important for your own analysis to create and have topologically correct data but also for people who you pass data on to They will be expecting your data and analysis results to be correct A Gentle Introduction to GIS 57 6 TOPOLOGY Topology rules Fortunately many common errors that can occur when digitising vector features can be prevented by topology rules that are implemented in many GIS applications Except for some special GIS data formats topology is usually not enforced by default Many common GIS like QGIS define topology as relationship rules and let the user choose the rules if any to be implemented in a vector layer The following list shows some examples of where topology rules can be defined for real world features in a vector map
104. phical data and is an important part of the GIS e AGIS Application normally consists of a menu bar toolbars a map view and a legend e Vector and raster data are geographical data used in a GIS application e Geographical data can have associated non geographical data Now you try Here are some ideas for you to try with your learners e Geography Describe the concept of GIS to your learners as outlined in this tutorial Ask them to try to think of 3 reasons why it might be handy to use a GIS instead of paper maps Here are some that we could think of A Gentle Introduction to GIS 7 1 INTRODUCING GIS GIS Applications allow you to create many different types of maps from the same data GIS is a great visualisation tool that can show you things about your data and how they are related in space e g those disease outbreaks we saw earlier Paper maps need to be filed and are time consuming to view The GIS can hold a very large amount of map data and make it quick and easy to find a place you are interested in e Geography Can you and your learners think of how raster data from satellites could be useful Here are some ideas we had During natural disasters raster data can be useful to show where the impacted areas are For example a recent satellite image taken during a flood can help to show where people may need rescuing Sometimes people do bad things to the the environment like dumping dangerous chem
105. possible to preserve all these characteristics at the same time in a map projection e A Coordinate reference system CRS defines with the help of coordinates how the two dimensional projected map is related to real locations on the earth e There are two different types of coordinate reference systems Geographic Coordinate Sys tems and Projected Coordinate Systems e On the Fly projection is a functionality in GIS that allows us to overlay layers even if they are projected in different coordinate reference systems Now you try Here are some ideas for you to try with your learners e Start QGIS and load two layers of the same area but with different projections and let your pupils find the coordinates of several places on the two layers You can show them that it is not possible to overlay the two layers Then define the coordinate reference system as Geographic WGS 84 inside the Project Properties Dialog and activate the check box enable On the fly CRS transformation Load the two layers of the same area again and let your pupils see how On the fly projection works e You can open the Project Properties Dialog in QGIS and show your pupils the many different Coordinate Reference Systems so they get an idea of the complexity of this topic With On the fly CRS transformation enabled you can select different CRS to display the same layer in different projections Something to think about If you don t have a computer ava
106. r Be E El Eis Si Bi 1 1 I 1 l I I I l I 1 i I I l I i I 1 I 1 I l l I i i I I ll I 1 i I l I I i i I 1 i I ll j I i I 1 l l I i I l I I 335 36S I I i I 35 and with its northing y value and easting x value in meters The northing value is the distance of the position from the equator in meters The easting value is the distance from the central meridian longitude of the used UTM zone For UTM zone 35S it is 27 degrees East as shown in Figure 60 Furthermore because we are south of the equator and negative values are not allowed in the UTM coordinate reference system we have to add a so called false northing value of 10 000 000m to the northing y value and a false easting value of 500 000m to the easting x value This sounds difficult so we will do an example that shows you how to find the correct UTM 35S coordinate for the Area of Interest The northing y value The place we are looking for is 3 550 000 meters south of the equator so the northing y value gets a negative sign and is 3 550 000m According to the UTM definitions we have to add a false northing value of 10 000 000m This means the northing y value of our coordinate is 6 450 000m 3 550 000m 10 000 000m The easting x value First we have to find the central meridian longitude for the UTM zone 35S As we can see in 71 i
107. r understand A Gentle Introduction to GIS 42 GIS FOR EDUCATORS Figure 39 A digitising table and puck are used by GIS professionals when they want to digitise features from existing maps A Gentle Introduction to GIS 43 4 DATA CAPTURE the data you have captured when you look at the map Common problems things to be aware of If you are digitising using a backdrop raster layer such as an aerial photograph or satellite image it is very important that the raster layer is properly georeferenced A layer that is georeferenced properly displays in the correct position in the map view based on the GIS Application s internal model of the earth We can see the effect of a poorly georeferenced image in Figure 40 Figure 40 The importance of using properly georeferenced raster images for heads up digitising On the left we can see the image is properly georegistered and the road features in orange overlap perfectly If the image is poorly georeferenced as shown on the right the features will not be well aligned Worse still if the image on the right is used as a reference when capturing new features the newly captured data will be inaccurate Also remember that it is important that you are zoomed in to an appropriate scale so that the vector features you create are useful As we saw in the previous topic on vector geometry it is a bad idea to digitise your data when you are zoomed out to a scale of 1 1000 000 if you inte
108. re 23 earlier in this topic we showed contours all drawn with the same colour Adding colour to the contours can help us to interpret the meanings of contours For example we can draw low lying areas with one colour mid altitude areas A Gentle Introduction to GIS 26 GIS FOR EDUCATORS with another and high altitude areas with a third Figure 26 The height attribute of contours can be used to separate the contours into 3 classes Contours between 980m and 1120m will be drawn in brown those between 1120m and 1240m in green and those between 1240m and 1500m in purple Layer Properties General Symbology Metadata Labels Actions Attributes Legend type Graduated Symbol Transparency 0 Classification field HEIGHT Mode Quantiles Number of classes 3 E Classify Delete class 980 000000 1120 000000 1120 000000 1240 000000 240 000000 E Label Style Options Outline style Solid ine Outline color p Outline width 0 26 Fill color ans Fill style mSolid Restore Default Style Save As Default Load Style Save Style Her Cancel Jok Figure 27 Our map after setting graduated colours for our contours y Setting colours based on discrete groups of attribute values is called Graduated Symbology in QGIS The process is shown in Figure 26 and 27 Graduated symbols are most useful when you want to show clear differences between features with attribute
109. re 58 on the right side Every point that is expressed in spherical coordinates can be expressed as an X Y Z coordinate Figure 58 Two and three dimensional coordinate reference systems A xelylz A projected coordinate reference system in the southern hemisphere south of the equator normally has its origin on the equator at a specific Longitude This means that the Y values increase south wards and the X values increase to the West In the northern hemisphere north of the equator the Origin is also the equator at a specific Longitude However now the Y values increase northwards and the X values increase to the East In the following section we describe a projected coordinate reference system called Universal Transverse Mercator UTM often used for South Africa A Gentle Introduction to GIS 69 7 COORDINATE REFERENCE SYSTEMS Universal Transverse Mercator UTM CRS in detail The Universal Transverse Mercator UTM coordinate reference system has its origin on the equator at a specific Longitude Now the Y values increase Southwards and the X values increase to the West The UTM CRS is a global map projection This means it is generally used all over the world But as already described in the section accuracy of map projections above the larger the area for example South Africa the more distortion of angular conformity distance and area occur To avoid too much distortion the world is divided
110. re and allow you to work with digital data A software program that forms part of the GIS is called a GIS Application With a GIS application you can open digital maps on your computer create new spatial information to add to a map create printed maps customised to your needs and perform spatial analysis Let s look at a little example of how GIS can be useful Imagine you are a health worker and you make a note of the date and place of residence of every patient you treat Table 1 Notes of date and place of residence of patients Longitude Latitude Disease Date 26 870436 31 909519 Mumps 13 12 2008 26 868682 31 909259 Mumps 24 12 2008 26 867707 31 910494 Mumps 22 01 2009 26 854908 31 920759 Measles 11 01 2009 26 855817 31 921929 Measles 26 01 2009 26 852764 31 921929 Measles 10 02 2009 26 852764 31 921929 Measles 22 02 2009 26 869072 31 911988 Mumps 02 02 2009 26 863354 31 916406 Chicken Pox 26 02 2009 A Gentle Introduction to GIS 1 INTRODUCING GIS If you look at the table above you will quickly see that there were a lot of measles cases in January and February Our health worker recorded the location of each patient s house by noting its latitude and longitude in the table Using this data in a GIS Application we can quickly understand a lot more about the patterns of illness Figure 1 Example showing disease records in a GIS application It is easy to see that the mumps pa
111. referred to as setting feature symbology Attribute data can also be useful when creating map labels Most GIS Applications will have a facility to select an attribute that should be used to label each feature Figure 22 In a GIS Application we can draw features differently depending on their attributes On the left we have drawn house polygons with the same colour as the roof attribute On the right we colour coded houses according to whether they have a balcony or not Quant GS OO Kre Eastericapevertore x File Edit View Layer Settings Plugins Tools Help File Edit View Layer Settings Plugins Tools Help y g ig add KELLES BREA aadd KEELES GARRO 72 2 OAKO ER D3 wa AAAA SI E X Q0 Sh wae AAA 4G Q2Qa Q080 YR SeSBFRR ORARJQQAO Yi SeSORR Legend ex El o eme avy Legend ex a o anis V Y 3 Building Points Y oy Trees v VE Roads 0133 Y amp Road Outlines Y Water Bodies Y amp Rivers Y Tx Spot Height Y Tx Spot Height v Bao y Bao Y amp Contours Y Ne Contours Building Areas y Building Areas y River Areas 91388 y River Areas 1388 a a aGIs 2009 QGIS 2009 26 06733 32 08643 Scale 1 8296 v Render ig 26 05662 32 09212 Scale 1 8296 v Render is 4 h If you have ever searched a map for a place name or a specific feature you will know how time consuming it can be Having attribute data can make searching for a specific feature
112. rent geometry types Now split your learners into groups and assign each group a few features to capture Have them symbolise their layers so that they are more meaningful to look at Combine the layers from all the groups to create a nice map of your school and its surroundings e Find a local river and take water samples along its length Make a careful note of the position of each sample using a GPS or by marking it on a toposheet For each sample take measurements such as pH dissolved oxygen etc Capture the data using the GIS application and make maps that show the samples with a suitable symbology Could you identify any areas of concern Was the GIS Application able to help you to identify these areas Something to think about If you don t have a computer available you can follow the same process by using transparency sheets and a notebook Use an aerial photo orthosheet or satellite image printout as your background layer Draw columns down the page in your notebook and write in the column headings for each attribute field you want to store information about Now trace the geometry of features onto the transparency sheet writing a number next to each feature so that it can be identified Now write the same number in the first column in your table in your notebook and then fill in all the additional information you want to record A Gentle Introduction to GIS 45 4 DATA CAPTURE Further reading Website http ww k12scie
113. rtain projection when you start the GIS and all layers that you then load no matter what coordinate reference system they have will be automatically displayed in the projection you defined This functionality allows you to overlay layers within the map window of your GIS even though they may be in different reference systems Common problems things to be aware of The topic map projection is very complex and even professionals who have studied geography geodetics or any other GIS related science often have problems with the correct definition of map projections and coordinate reference systems Usually when you work with GIS you already have projected data to start with In most cases these data will be projected in a certain CRS so you don t have to create anew CRS or even re project the data from one CRS to another That said it is always useful to have an idea about what map projection and CRS means What have we learned Let s wrap up what we covered in this worksheet e Map projections portray the surface of the earth on a two dimensional flat piece of paper or computer screen A Gentle Introduction to GIS 72 GIS FOR EDUCATORS e There are global map projections but most map projections are created and optimized to project smaller areas of the earth s surface e Map projections are never absolutely accurate representations of the spherical earth They show distortions of angular conformity distance and area It is im
114. rth by giving someone your Longitude X and Latitude Y If you make a similar measurement for a tree or a telephone pole and marked it on a map you will have created a point feature Since we know the earth is not flat it is often useful to add a Z value to a point feature This describes how high above sea level you are Polyline features in detail Where a point feature is a single vertex a polyline has two or more vertices The polyline is a continuous path drawn through each vertex as shown in Illustration 3 above When two vertices are A Gentle Introduction to GIS 11 2 VECTOR DATA joined a line is created When more than two are joined they form a line of lines or polyline A polyline is used to show the geometry of linear features such as roads rivers contours footpaths flight paths and so on Sometimes we have special rules for polylines in addition to their basic geometry For example contour lines may touch e g ata cliff face but should never cross over each other Similarly polylines used to store a road network should be connected at intersections In some GIS applications you can set these special rules for a feature type e g roads and the GIS will ensure that these polylines always comply to these rules If a curved polyline has very large distances between vertices it may appear angular or jagged depending on the scale at which it is viewed see Figure 12 Because of this it is important that p
115. s a backdrop layer You can then use this layer as a reference map or even trace the features off the raster layer into your vector layer if they are visible This process is known as heads up digitising and is shown in Figure 38 A Gentle Introduction to GIS 41 4 DATA CAPTURE Figure 38 Heads up digitising using a satellite image as a backdrop The image is used as a reference for capturing polyline features by tracing over them O Quantum GIS 1 0 2 Kore B BAO arse re pd Qn am Te Ueageee TEA CEA Digitising using a digitising table Another method of capturing vector data is to use a digitising table This approach is less commonly used except by GIS professionals and it requires expensive equipment The process of using a digitising table is to place a paper map on the table The paper map is held securely in place using clips Then a special device called a puck is used to trace features from the map Tiny cross hairs in the puck are used to ensure that lines and points are drawn accurately The puck is connected to a computer and each feature that is captured using the puck gets stored in the computer s memory You can see what a digitising puck looks like in Figure 39 After your features are digitised Once your features are digitised you can use the techniques you learned in the previous Topic to set the symbology for your layer Choosing an appropriate symbology will allow you to bette
116. s there is no single projection that is able to represent the Earth perfectly for any area in the world Every projection has advantages and disadvantages To be able to create maps as precisely as possible people have studied modified and produced many different kinds of projections In the end almost every country has developed its own map projection with the goal of improving the map accuracy for their territorial area see Figure 66 Figure 66 The world in different projections A Mollweide Equal Area projection left a Plate Carree Equidistant Cylindrical projection on the right With this in mind we can now understand why it makes sense to add the name of the projection on a map It allows the reader to see quickly if one map can be compared with another For example features on a map in a so called Equal Area projection appear very different to features projected in a Cylindrical Equidistant projection see Figure 66 Map projection is a very complex topic and we cannot cover it completely here You may want to take a look at our previous topic Coordinate Reference Systems if you want to know more about it Common problems things to be aware of It is sometimes difficult to create a map that is easy to understand and well laid out whilst still showing and explaining all the information that the reader needs to know To achieve this you need to create an ideal arrangement and composition of all the map elements
117. t is 27 degrees East The place we are looking for is 85 000 meters West from the central meridian Just like the northing value the easting x value gets a negative sign giving a result of A Gentle Introduction to GIS 71 7 COORDINATE REFERENCE SYSTEMS 85 000m According to the UTM definitions we have to add a false easting value of 500 000m This means the easting x value of our coordinate is 415 000m 85 000m 500 000m Finally we have to add the zone number to the easting value to get the correct value As a result the coordinate for our Point of Interest projected in UTM zone 35S would be written as 35 415 000mE 6 450 000mN In some GIS when the correct UTM zone 35S is defined and the units are set to meters within the system the coordinate could also simply appear as 415 000 6 450 000 On The Fly Projection As you can probably imagine there might be a situation where the data you want to use in a GIS are projected in different coordinate reference systems For example you might get a vector layer showing the boundaries of South Africa projected in UTM 35S and another vector layer with point information about rainfall provided in the geographic coordinate system WGS 84 In GIS these two vector layers are placed in totally different areas of the map window because they have different projections To solve this problem many GIS include a functionality called On the fly projection It means that you can define a ce
118. ted above and you may publicly display copies COPYING IN QUANTITY If you publish printed copies or copies in media that commonly have printed covers of the Document numbering more than 100 and the Document s license notice requires Cover Texts you must enclose the copies in covers that carry clearly and legibly all these Cover Texts Front Cover Texts on the front cover and Back Cover Texts on the back cover Both covers must also clearly and legibly identify you as the publisher of these copies The front cover must present the full title with all words of the title equally prominent and visible You may add other material on the covers in addition Copying with changes limited to the covers as long as they preserve the title of the Document and satisfy these conditions can be treated as verbatim copying in other respects If the required texts for either cover are too voluminous to fit legibly you should put the first ones listed as many as fit reasonably on the actual cover and continue the rest onto adjacent pages If you publish or distribute Opaque copies of the Document numbering more than 100 you must either include a machine readable Transparent copy along with each Opaque copy or state in or with each Opaque copy a computer network location from which the general network using public has access to download using public standard network protocols a complete Transparent copy of the Document free of added material If you use
119. tell the difference between rivers roads and contours using the map on the left Using 0 49440 01 d 01155 FA degrees 41129 1115 LE MD A o DA y aitaset026 ld 1212 28 y a 1247 e1154 41205 p e 91146 51127 N x a 7 0008 iho In this topic we will look at how attribute data can help us to make interesting and informative maps In the previous topic on vector data we briefly explained that attribute data are used to describe vector features Take a look at the house pictures in Figure 20 below The geometry of these house features is a polygon based on the floor plan of the house the attributes we have recorded are roof colour whether there is a balcony and the year the house was built Note that attributes don t have to be visible things they can describe things we know about the feature such as the year it was built In a GIS Application we can represent this feature type in a houses polygon layer and the attributes in an attribute table see Figure 21 A Gentle Introduction to GIS 21 3 VECTOR ATTRIBUTE DATA Figure 20 Every feature has characteristics that we can describe These can be visible things or things we know about the feature e g year built Roof Colour Red Has balcony Yes Year Built 2000 Roof Colour Black Has balcony No Year Built 2002 Figure 21 A houses layer House features have attributes that describe the houses roof colour and other properties T
120. the files for that layer So in the case of the trees layer shown in 32 you would need to give the person trees shp trees shx trees dbf trees prj and trees qml Figure 32 The files that make up a trees shapefile as seen in the computer s file manager 5 C Program Files Quantum GIS gisdata local i J 0 x File Edit view Favorites Tools Help Ap Q back x gt Y ce Search gt Folders ID E x 1 ER Address S C Program Files Quantum GISigisdatallocal Go x Folders El 5 Quantum GIS sl El 5 bin El E doc 5 gisdata E E alaska D ecape O local D sa B it8n a icons 5 images D include B lib trees dbf trees prj 4 trees shp trees shx x e Ratu MaR i las objects Disk free space 19 0 GB 2 01 MB y My Computer A Many GIS Applications are also able to store digital data inside a database In general storing GIS data in a database is a good solution because the database can store large amounts of data efficiently and can provide data to the GIS Application quickly Using a database also allows many people to work with the same vector data layers at the same time Setting up a database to store GIS data is more complicated than using shapefiles so for this topic we will focus on creating and editing shapefiles Planning before you begin Before you can create a new vector layer which will be stored in a shapefile
121. tial analysis tools for calculating feature statistics and car rying out geoprocessing activities as data interpolation In hydrology users will likely emphasize the importance of terrain analysis and hydrological modelling modelling the movement of water over and in the earth In wildlife management users are interested in analytical functions dealing with wildlife point locations and their relationship to the environment Each user will have different things they are interested in depending on the kind of work they do Spatial interpolation in detail Figure 74 Temperature map interpolated from South African Weather Stations Temperatures in South Africa Pie on 15 April 2009 at 11am Spatial interpolation is the process of using points with known values to estimate values at other unknown points For example to make a precipitation rainfall map for your country you will not A Gentle Introduction to GIS 91 10 SPATIAL ANALYSIS INTERPOLATION find enough evenly spread weather stations to cover the entire region Spatial interpolation can estimate the temperatures at locations without recorded data by using known temperature readings at nearby weather stations see Figure 74 This type of interpolated surface is often called a statistical surface Elevation data precipitation snow accumulation water table and population density are other types of data that can be computed using interpolation Because of high cost and lim
122. tients all live close to each other Quantum GIS 1 0 0 Kore EasternGape File Edit View Layer Plugins Tools Help o _ a i DS sS 548800 VLAS WLAN FOOD 2 OOS Ke Sw ta alalu BM E SEN RAR L nnna Ss eRonoo aa 0 Legend as a gt nal g a y ecape disease example Chicken Pox E3 Measles i O Mumps a la E ve rivers Ds or 5 vd za_roads La bk HIGHWAY T i de it X MAIN ROADS OTHER SECONDARY J i STREET E Er Ml railway o i DE a Jl za highways 5 y Eastern Cape Province Er 8 Population by Municipa e 0 001 96977 100 96977 100 193954 200 a 193954 200 290931 300 290931 300 387908 400 BE 387908 400 484885 500 a i BE 484885 500 581862 600 ME 581862 600 678839 700 a ME 678839 700 775816 800 M_775816 800 872793 900 4 QGIS 2008 95 26 84592 31 90445 Scale 112073 y Render More about GIS GIS is a relatively new field it started in the 1970 s lt used to be that computerised GIS was only available to companies and universities that had expensive computer equipment These days anyone with a personal computer or laptop can use GIS software Over time GIS Applications have also become easier to use it used to require a lot of training to use a GIS Application but now it is much easier to get started in GIS even for amateurs
123. tle in detail The map title is very important because it is usually the first thing a reader will look at on a map It can be compared with a title in a newspaper It should be short but give the reader a first idea of what the map is about Map Border in detail The map border is a line that defines exactly the edges of the area shown on the map When printing a map with a graticule which we describe further down you often find the coordinate information of the graticule lines along the border lines as you can see in Figure 62 Map Legend in detail A map is a simplified representation of the real world and map symbols are used to represent real objects Without symbols we wouldn t understand maps To ensure that a person can correctly read a map a map legend is used to provide a key to all the symbols used on the map Figure 62 Two maps from the same area both with a water body in the background but with different themes map symbols and colours in the legend UA MAP gt gt A Gentle Introduction to GIS 76 GIS FOR EDUCATORS It is like a dictionary that allows you to understand the meaning of what the map shows A map legend is usually shown as a little box in a corner of the map It contains icons each of which will represent a type of feature For example a house icon will show you how to identify houses on the map see Figure 62 You can also use different symbols and icons in your legend to show different
124. topology rules topology errors search radius snaping distance simple feature Overview Topology expresses the spatial relationships between connecting or adjacent vector features points polylines and polygons in a GIS Topological or topology based data are useful for detecting and correcting digitising errors e g two lines in a roads vector layer that do not meet perfectly at an intersection Topology is necessary for carrying out some types of spatial analysis such as network analysis Imagine you travel to London On a sightseeing tour you plan to visit St Paul s Cathedral first and in the afternoon Covent Garden Market for some souvenirs Looking at the Underground map of London see Figure 47 you have to find connecting trains to get from Covent Garden to St Paul s This requires topological information data about where it is possible to change trains Looking at a map of the underground the topological relationships are illustrated by circles that show connectivity Changing trains at stations allows you to move from one connected part of the network to another Figure 47 Topology of London Underground Network King s Cross St Pancras O Green Park XY Cross tek Knightsbridge O Paddington hh Covent Marble ez Garden Lancaster Arch ircus Leicester O Queensway Gate all Charing gt High Street Q Kensington IS y or Gloucester South Road Kensington Hyde P
125. troduction to GIS 96 GIS FOR EDUCATORS What s next This is the final worksheet in this series We encourage you to explore QGIS and use the QGIS manual to discover all the other things you can do with GIS software A Gentle Introduction to GIS 97 Authors and Contributors Tim Sutton Editor 8 Lead Author Tim Sutton is a developer and project steering committee member of the Quantum GIS project He is passionate about seeing GIS being Freely available to everyone Tim is also a founding member of Linfiniti Consulting CC a small business set up with the goal of helping people to learn and use open source GIS software Web http linfiniti com Email tim linfiniti com Otto Dassau Assistant Author Otto Dassau is the documentation maintainer and project steering committee member of the Quantum GIS project Otto has consider able experience in using and training people to use Free and Open Source GIS software Web http gbd consult de Email dassau gbd consult de Marcelle Sutton Project Manager Marcelle Sutton studied english and drama and is a qualified teacher Marcelle is also a founding member of Linfiniti Consulting CC a small business set up with the goal of helping people to learn and use open source GIS software Web http linfiniti com Email marcelle linfiniti com Lerato Nsibande Lerato is a grade 12 scholar living in Pretoria Lerato learns Geog raphy at school and has enjoyed learning GIS
126. ts are stored in special file formats that record all the relationships between features Most commonly used vector data formats use something called Simple Features which also consists of point line and polygon features Simple feature datasets are mainly designed for simplicity and for fast rendering but not for data analysis that require topology such as finding routes across a network Many GIS applications A Gentle Introduction to GIS 59 6 TOPOLOGY are able to show topological and simple feature data together and some can also create edit and analyse both What have we learned Let s wrap up what we covered in this worksheet e Topology shows the spatial relation of neighbouring vector features Topology in GIS is provided by topological tools Topology can be used to detect and correct digitizing errors e For some tools such as network analysis topological data is essential Snapping distance and search radius help us to digitise topologically correct vector data Simple feature data is not a true topological data format but it is commonly used by GIS applications Now you try Here are some ideas for you to try with your learners e Mark your local bus stops on a toposheet map and then task your learners to find the shortest route between two stops e Think of how you would create vector features in a GIS to represent a topological road network of your town What topological rules are important and wh
127. ttributes describe the feature Polyline attributes describe the feature Polyline Geometry a series of connected vertices that do not form an enclosed shape Id Name Description Polygon Geometry a series of connected vertices that do form an enclosed shape k x x Polygon attributes describe the feature Id Name Description 1 Tree Outside our classroom 2 Light post At the school entrance 1 Footpath 1 From class to the playground 2 Footpath 2 From the school gate to the hall 1 School Boundary Fenceline for the school 2 Sports Field We play soccer here b A polyline is a sequence of joined vertices Each vertex has an X Y and optionally Z coordinate Attributes de scribe the polyline c A polygon like a polyline is a se quence of vertices However in a poly gon the first and last vertices are al ways at the same position a A point feature is described by its X Y and optionally Z coordinate The point attributes describe the point e g if itis a tree or a lamp post Looking back at the picture of a landscape we showed you further up you should be able to see the different types of features in the way that a GIS represents them now see Figure 11 Point features in detail The first thing we need to realise when talking about point features is that what we describe as a point in GIS is a matter of opinion and often dependent
128. tude are measured from zero at the equator to ninety at the north pole In the southern hemisphere degrees of latitude are measured from zero at the equator to ninety degrees at the south pole To simplify the digitisation of maps degrees of latitude in the southern hemisphere are often assigned negative values 0 to 90 Wherever you are on the earth s surface the distance between the lines of latitude is the same 60 nautical miles See Figure 57 for a pictorial view Figure 57 Geographic coordinate system with lines of latitude parallel to the equator and lines of longitude with the prime meridian through Greenwich 180 450 120 90 80 30 0 30 60 90 120 150 180 Lines of longitude on the other hand do not stand up so well to the standard of uniformity Lines of longitude run perpendicular to the equator and converge at the poles The reference line for lon gitude the prime meridian runs from the North pole to the South pole through Greenwich England Subsequent lines of longitude are measured from zero to 180 degrees East or West of the prime meridian Note that values West of the prime meridian are assigned negative values for use in digital mapping applications See Figure 57 for a pictorial view At the equator and only at the equator the distance represented by one line of longitude is equal to the distance represented by one degree of latitude As you move towards the poles the distance between lines of longi
129. tude becomes progressively less until at the exact location of the pole all 360 of longitude are represented by a single point that you could put your finger on you probably would want to wear gloves though Using the geographic coordinate system we have a grid of lines dividing the earth into squares that cover approximately 12363 365 square kilometres at the equator A Gentle Introduction to GIS 68 GIS FOR EDUCATORS a good start but not very useful for determining the location of anything within that square To be truly useful a map grid must be divided into small enough sections so that they can be used to describe with an acceptable level of accuracy the location of a point on the map To accomplish this degrees are divided into minutes and seconds There are sixty minutes in a degree and sixty seconds in a minute 3600 seconds in a degree So at the equator one second of latitude or longitude 30 87624 meters Projected coordinate reference systems A two dimensional coordinate reference system is commonly defined by two axes At right angles to each other they form a so called XY plane see Figure 58 on the left side The horizontal axis is normally labelled X and the vertical axis is normally labelled Y In a three dimensional coordinate reference system another axis normally labelled Z is added It is also at right angles to the X and Y axes The Z axis provides the third dimension of space see Figu
130. ture e g Secondary Road Vertices the feature e g Municipal Dam y a eo Longtuae Y 25 aus coin e Longitude PI e Lat tei ea Longitude IP e 9 Latitude elt a 4 above sea level i Hi above sea level goang 5 above sea level A Gentle Introduction to GIS 18 GIS FOR EDUCATORS Now you try Here are some ideas for you to try with your learners e Using a copy of a toposheet map for your local area like the one shown in Figure 18 see if your learners can identify examples of the different types of vector data by highlighting them on the map e Think of how you would create vector features in a GIS to represent real world features on your school grounds Create a table of different features in and around your school and then task your learners to decide whether they would be best represented in the GIS as a point line or polygon See Table 1 below for an example Figure 18 Can you identify two point features and one polygon feature on this map TT LS TS A MERA FL AT jl I i Ta A PA de J e E ue Vo S ir wy l i vs gt r nm el PA 1 Sos j NA Ny N SN reini L E Y j 77 SS gt Sy A gt QM TP N y e Ae A y 1 Qe So JA DALE a RS ff a a y SEN mAN TLA j i 1 WWyco Wycombevale 5 Y TORR IA ZRP A J a ae A 7 iS Shia y E el ART AO aa Pit st Al ATL Ns x a A 7 K Pa J SPR TE SV Y E A
131. uch as Regularized Splines with Tension RST Krig ing or Trend Surface interpolation See the additional reading section below for a web link What have we learned Let s wrap up what we covered in this worksheet e Interpolation uses vector points with known values to estimate values at unknown locations to create a raster surface covering an entire area e The interpolation result is typically a raster layer e ltis important to find a suitable interpolation method to optimally estimate values for unknown locations e IDW interpolation gives weights to sample points such that the influence of one point on another declines with distance from the new point being estimated e TIN interpolation uses sample points to create a surface formed by triangles based on nearest neighbour point information A Gentle Introduction to GIS 95 10 SPATIAL ANALYSIS INTERPOLATION Now you try Here are some ideas for you to try with your learners e The Department of Agriculture plans to cultivate new land in your area but apart from the char acter of the soils they want to know if the rainfall is sufficient for a good harvest All the information they have available comes from a few weather stations around the area Create an interpolated surface with your learners that shows which areas are likely to receive the highest rainfall e The tourist office wants to publish information about the weather conditions in January and February They
132. variations in colour you can see in the grass When you are trying to represent large areas with continuously changing values raster data can be a better choice Using raster data is a solution to these problems Many people use raster data as a backdrop to be used behind vector layers in order to provide more meaning to the vector information The human eye is very good at interpreting images and so using an image behind vector layers results in maps with A Gentle Introduction to GIS 48 GIS FOR EDUCATORS a lot more meaning Raster data is not only good for images that depict the real world surface e g satellite images and aerial photographs they are also good for representing more abstract ideas For example rasters can be used to show rainfall trends over an area or to depict the fire risk ona landscape In these kinds of applications each cell in the raster represents a different value e g risk of fire on a scale of one to ten An example that shows the difference between an image obtained from a satellite and one that shows calculated values can be seen in Figure 43 Figure 43 True colour raster images left are useful as they provide a lot of detail that is hard to capture as vector features but easy to see when looking at the raster image Raster data can also be non photographic data such as the raster layer shown on the right which shows the calculated average minimum temperature in the Western Cape for the month of M
133. ve attributes The attributes describe each polygon For example a dam may have attributes for depth and water quality Vector data in layers Now that we have described what vector data is let s look at how vector data is managed and used in a GIS environment Most GIS applications group vector features into layers Features in a layer have the the same geometry type e g they will all be points and the same kinds of attributes e g information about what species a tree is for a trees layer For example if you have recorded the positions of all the footpaths in your school they will usually be stored together on the computer hard disk and shown in the GIS as a single layer This is convenient because it allows you to hide or show all of the features for that layer in your GIS application with a single mouse click Editing vector data The GIS application will allow you to create and modify the geometry data in a layer a process called digitising which we will look at more closely in a later tutorial If a layer contains polygons e g farm dams the GIS application will only allow you to create new polygons in that layer Similarly if you want to change the shape of a feature the application will only allow you to do it if the changed shape is correct For example it won t allow you to edit a line in such a way that it has only one vertex remember in our discussion of lines above that all lines must have at least two vertices Creating
134. w problems or concerns See http www gnu org copyleft Each version of the License is given a distinguishing version number If the Document specifies that a particular numbered version of this License or any later version applies to it you have the option of following the terms and conditions either of that specified version or of any later version that has been published not as a draft by the Free Software Foundation If the Document does not specify a version number of this License you may choose any version ever published not as a draft by the Free Software Foundation A Gentle Introduction to GIS 105 10 SPATIAL ANALYSIS INTERPOLATION ADDENDUM How to use this License for your documents To use this License in a document you have written include a copy of the License in the document and put the following copyright and license notices just after the title page Copyright YEAR YOUR NAME Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 2 or any later version published by the Free Software Foundation with no Invariant Sections no Front Cover Texts and no Back Cover Texts A copy of the license is included in the section entitled GNU Free Documentation License If you have Invariant Sections Front Cover Texts and Back Cover Texts replace the with Texts line with this with the Invariant Sections being LIST THEI
135. wing the data in a GIS For example slivers can occur when the edges of two polygon areas don t meet properly see Figure 15 Overshoots can occur when a line feature such as a road does not meet another road exactly at an intersection Undershoots can occur when a line feature e g a river does not exactly meet another feature to which it should be connected Figure 16 demonstrates what undershoots and overshoots look like Because of these types of errors it is very important to digitise data carefully and accurately In the upcoming topic on topology we will examine some of these types of errors in more detail Figure 15 Slivers occur when the vertices of two polygons do not match up on their borders At a small scale e g 1 on left you may not be able to see these errors At a large scale they are visible as thin strips between two polygons 2 on right 01115 ALZA PSN gt 4 moas Y i UN f li qq 1128 f s 1247 of 154 ff f X A 91205 E 01384 Ay as Pg tt27 Ry nenea i A f 1104 l 91029 91262 e1128 1139 Cc LA dd MARIS INNA A Gentle Introduction to GIS 16 GIS FOR EDUCATORS Figure 16 Undershoots 1 occur when digitised vector lines that should connect to each other don t quite touch Overshoots 2 happen if a line ends beyond the line it should connect to s a QGIS 2009 What have we learned Let s wrap up what we covered in this worksheet Vector d
136. you are building your own skills freeing money to be spent on important things like food and shelter and boosting our own economy By sponsoring the creation of this resource the DLA has created a foundation to which young minds can be exposed Exciting possibilities lie ahead when principles of free sharing of knowledge and data are embraced For this we give our heartfelt thanks to the DLA We hope you enjoy using and learning QGIS in the spirit of Ubuntu Aw lh Tim Sutton April 2009 Contents Title Copyright information A word from the editor Table of Contents 1 Introducing GIS 1 A A A Getting a GIS Application for your own COMPputer S o e OI a AR AR a e ee Ba G What have we learned Now VOUT ecca ASSP PH GEESE dew OAS GS PS SAGES ESS HES EE ED SS Someone MR GOO 24462445 ea ot oe bee iaa FUMA reading oca Bk eye So ee a BN ee AA ew a Whats cS eb ee Ree Se CER AE RES a a eRe ee EROS PES OS Gs Vector Data Overview o Point features in detail Polyline features in detail Polygon features in detail Vector data in layers Editing vector data Scale and vector data Sympology gt kao a hE SER aS EES What can we do with vector data in a GIS Common problems with vector data What have we learned Now YOUTY 6244484444 4445 84 2 Something to think about
137. you need know what the geometry of that layer will be point polyline or polygon and you need to know what the attributes of that layer will be Let s look at a few examples and it will become clearer how to go about doing this A Gentle Introduction to GIS 35 4 DATA CAPTURE Example 1 Creating a tourism map Imagine that you want to create a nice tourism map for your local area Your vision of the final map is a 1 50 000 toposheet with markers overlaid for sites of interest to tourists First let s think about the geometry We know that we can represent a vector layer using point polyline or polygon features Which one makes the most sense for our tourism map We could use points if we wanted to mark specific locations such as look out points memorials battle sites and so on If we wanted to take tourists along a route such as a scenic oute through a mountain pass it might make sense to use polylines If we have whole areas that are of tourism interest such as a nature reserve or a cultural village polygons might make a good choice As you can see it s often not easy to know what type of geometry you will need One common approach to this problem is to make one layer for each geometry type you need So for example if you look at digital data provided by the Chief Directorate Surveys and Mapping South Africa they provide a river areas polygons layer and a rivers polyline layer They use the river areas polygons to repres

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