Introduction to QGIS: Student Workbook

Transcription

1 2016 Introduction to QGIS: Student Workbook Created by: MARK DE BLOIS, CEO / FOUNDER, UPANDE LIMITED WITH SUPPORT FROM THE WORLD BANK AND THE UK DEPARTMENT FOR INTERNATIONAL DEVELOPMENT (DFID)

2 Module 3: Introduction to QGIS Student s Workbook Contents Introduction Lesson 1: Introduction to QGIS How to use QGIS Browser Lesson 2: Adding Simple Layers to a GIS file in QGIS Desktop Lesson 2: Using Plugins in QGIS Lesson 3: Search and Download OpenStreetMap Data Read More 1

3 Introduction In the previous module, you were introduced to the GIS tools. In this module, you will learn more about Quantum GIS which is often referred to as QGIS. At the end of this module, you will be able to: Open GIS files in QGIS browser Add layers to GIS files in QGIS Add plugins to QGIS Import and view OpenStreetMap data in QGIS 2

4 Lesson 1: Introduction to QGIS QGIS is a free and open-source GIS application. You can download QGIS from: When you install QGIS, you will find its two components: QGIS Desktop is the main tool for mapping and GIS analysis. QGIS Browser helps you browse through available data for GIS purposes. How to use QGIS Browser To begin with, let s take a look at the features of the QGIS Browser. The QGIS browser screen is divided into two windows: 3

5 The window on the left is the directory, where data stored in various disks and folders can be accessed. Note that QGIS Browser directory only lists spatial data supported by QGIS. The window on the right is where a quick preview and facts about the data file you select is displayed. In this example, a file called contour.shp is selected in the directory on the left. The window on the right now shows the facts about this file across several tabs: Metadata tab provides basic information about the file Preview tab provides a visual preview of the data file 4

6 Attribute tab shows the fields and values in the data file 5

7 In the next lesson, you will learn more about using QGIS Desktop. 6

8 Lesson 2: Adding Simple Layers to a GIS file in QGIS Desktop For the purpose of this tutorial, we will use the Sudan Data folder, which contains the Sudan Data.qgs file. In case this folder is not available on your computer, please ask your trainer. NB1: Just the same way Microsoft word saves its documents with the extension.doc or.docx, The QGIS tool saves its files with the extension.qgs NB2: Layers in GIS represent different sets of data that can be combined to create a map. For example, the map of Sudan may include cities and town, rivers, mountains roads and the country s boundary. Each of the items listed (i.e. cities, towns, rivers, mountains, roads and country boundary) above are stored in GIS as different layers. Combination of these different features can then be referred to as a Map of Sudan. Here are the steps to create a simple map with QGIS: 1. Open QGIS. 2. Select Project > Open 7

9 3. In the window that opens, select the Sudan Data folder, and then click the file named Sudan Data.qgs 4. The file opens in QGIS. 8

10 5. Now go to Project > New Print Composer 6. In the small window that pops up, enter Sudan as the name of the map. Then, click OK. 9

11 7. A new window with a blank map appears. 8. Now click Layout > Add Map 9. Now click the left mouse button and drag the mouse pointer across the blank map to create a rectangle. The rectangle now displays the map. 10

12 10. Now let s try repositioning this map so that it is better displayed. In the Item panel on the right, scroll down and click Set to map canvas extent 11. Scroll back up again to Main properties. Now in the Scale field, enter and then click Update preview 11

13 12. The map is better adjusted on the screen, now let s add a title to the map. To do this, click Layout > Add Label 13. Back on the map canvas, draw a rectangle at the top using the mouse. 14. On the right panel, a new item will appear above Map 0, which by default it is labeled QGIS. Click this label. NB: The new item appears because the tool recorgnises that the user wants to add a layer, probably one of several, to the map. Hence every time step 13 above is 12

14 done, a new item will appear 15. Under Main Properties, type SUDAN MAP to give the map a title. 16. Now that we have added a title, let s add a North Arrow on the map. The purpose of the Arrow is for orientations purposes. This way we are able to note directions of different regions of the country on the map To do this, click Layout > Add Arrow 13

15 17. Back on the map canvas, hold left mouse button and draw a rectangle at the top left. 18. We will now add a legend to our map. To do this, click Layout > Add legend 19. Back on the map canvas, hold left mouse button and draw a rectangle at the bottom right corner. 14

16 20. Finally, add a scale bar to the map. Click Layout > Add Scalebar 21. Back on the map canvas, hold left mouse button and draw a rectangle at the bottom left. 22. Your final map should appear as shown here. Save the work by clicking on the save icon at the top left corner. 15

17 23. The map can be exported as an image, PDF or SVG. For this tutorial, let s export it as PDF. To do his, click Compose > Export as PDF. 16

18 Lesson 2: Using Plugins in QGIS A plugin is a program that can be easily installed and used as part of a software to improve its functionality. QGIS being an open source software allows users add plugins based on your requirements. You can use three types of plugins in QGIS: Core plugins are installed together with the QGIS (some may need to be enabled) External plugins can be found and installed from QGIS Plugin Repository Experimental plugins are available online for experimental purposes In QGIS, the Plugin Manager helps you work with plugins. In the next steps, we are going to install a Plugin to our QGIS tool. The Plugin will help us load other layers of data, specifically from Google maps, Bing maps or Openstreetmap, when we need to use them. Layers from these three sources are usually richer in content and we may at times need to use with the maps we are creating. To open the Plugin Manager, click Plugins > Manage and Install Plugins The Plugins window opens. 17

19 You can find the Search bar in this window to find a plugin. The left bar shows categories of plugins; All Plugins, Installed, and Not installed Based on the selection in the left bar, the window in the center shows a list of plugins The window on the right shows the quick description of the selected plugin in the list To better understand plugins, let s find and install a plugin plugin called Open Layers. To do this first type Open in the search box. As you start typing Open in the search box, you will see the search results below. 18

20 Click the OpenLayers Plugin. Next, click the Install plugin button as shown in the image below... 19

21 Upon installation, the plugin icon and name appear in the list as installed. 20

22 Lesson 3: Search and Download OpenStreetMap Data OpenStreetMap (OSM) is an open source mapping platform, which creates and distributes free geographic data for the world. You can access and use OpenStreetMap in QGIS. To do this OpenStreetMap, the OpenLayers plugin needs to be installed in QGIS. We already installed this plugin in the last lesson. To access OpenStreetMap, click Web > OpenLayers plugin > OpenStreetMap > OpenStreetMap 21

23 A world map will be loaded in the QGIS canvas. You can use the OSM place search which is automatically displayed on the left side of the canvas to search for places, say Khartoum. The map layer moves and centers around Khartoum. Use the Zoom tool at the bottom of the OSM place search to zoom and select your Area Of Interest (AOI). 22

24 You can also download the data displayed on this map. To download data, select Vector > OpenStreetMap > Download Data 23

25 The Download OpenStreetMap data opens. Under the Extent section select From map canvas. Next, in the Output section, select a folder to save the file, and name the output file as Khartoum.osm Notice that as the data is downloaded from OpenStreetMap it, the downloaded file has the.osm extension which is a text file in the OSM XML format. To use this file in QGIS, we need to convert it to a format suitable for QGIS. To do this, we go through the following steps, first select Vector > OpenStreetMap > Import Topology from XML NB:Topology, are the features seen on the map i.e roads, rivers etc. In our case we shall only be interested in the roads topology. 24

26 The OpenStreetMap Import window opens. In the Input XML file (.osm) section, select the downloaded Khartoum.osm file In the Output SpatiaLite DB file, name the output file as Khartoum.db Check the Create connection (SpatiaLite) after import box Finally, we will create SpatialLite geometry layers that can be viewed and analyzed in QGIS. A geometry layer is a file format that the QGIS tool can allow users to edit; a vector. Spatiallite, is a lighter format of Vectors designed for use on the web. The purpose of this next step is therefore to convert our earlier downloaded.osm data into a file format that QGIS can handle i.e we can edit, query etc. To do this, go to Vector > OpenStreetMap > Export Topology to SpatialLite 25

27 The Export OpenStreetMap topology to SpatiaLite window opens. 26

28 In this window: Click the button in the Input DB file section to browse and select the Khartoum.db file In the Export Type section, select Polylines (Open ways) In the Output layer name section, enter khartoum_ways In the Exported tags section, click Load from DB. o Note that GIS data has two parts - location and attributes. Since we are interested in the highway, name, and surface attributes of Khartoum.db file, we have selected this file. Check highway, name, and surface under the column Tag. Ensure Load into canvas when finished is checked, and then click OK. 27

29 Now back on your main Map canvas, uncheck the OpenStreetMap layer. You will see a new layer named khartoum_ways loaded in QGIS. See Image below. We can also view the attributes of this layer. To do this, right-click on khartoum_ways layer and select Open Attribute Table. 28

30 The table shows the Highway, name, and surface tags we selected earlier. Note that the information about the type of highway, its name, and surface type has been displayed. 29

31 You will note that some highways have asphalt listed under the surface column. We can use a query to work with the highways with asphalt surfaces only. To do this, while on the attributes table window: Click on the expression function button Enter the expression surface = asphalt Click Select 30

32 The attribute table now highlights the rows that correspond to the asphalt surface. 31

33 Minimise the Attribute table window and click inside the main Map window. Do not close the Select by expression window since you may need it later. Now right-click the khartoum_ways layer, and select Save As NB: The aim is to save the asphalt roads we had selected. The Save vector layer as window opens. In this window: 32

34 Retain the format as ESRI Shapefile In the Save as section, browse to the location where you will save the file and name the file as Khartoum_Selected ways.shp Ensure you check Save only selected features Click OK The layer saved now only will show roads whose surface is asphalt. 33

35 Commented [1]: Update screenshot with new layer name Using the identity tool, you can also view the attributes of any particular road. To use the tool, click on the icon shown (located at the top, on the icons menu) to select it. Now click on any feature on the map. What happens? 34

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37 Read More Access more tutorials on QGIS: Learn about coordinate systems: See more case studies where QGIS is used: Get an overview of OpenStreetMap: 36