Table of Contents for
QGIS: Becoming a GIS Power User

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition QGIS: Becoming a GIS Power User by Alexander Bruy Published by Packt Publishing, 2017
  1. Cover
  2. Table of Contents
  3. QGIS: Becoming a GIS Power User
  4. QGIS: Becoming a GIS Power User
  5. QGIS: Becoming a GIS Power User
  6. Credits
  7. Preface
  8. What you need for this learning path
  9. Who this learning path is for
  10. Reader feedback
  11. Customer support
  12. 1. Module 1
  13. 1. Getting Started with QGIS
  14. Running QGIS for the first time
  15. Introducing the QGIS user interface
  16. Finding help and reporting issues
  17. Summary
  18. 2. Viewing Spatial Data
  19. Dealing with coordinate reference systems
  20. Loading raster files
  21. Loading data from databases
  22. Loading data from OGC web services
  23. Styling raster layers
  24. Styling vector layers
  25. Loading background maps
  26. Dealing with project files
  27. Summary
  28. 3. Data Creation and Editing
  29. Working with feature selection tools
  30. Editing vector geometries
  31. Using measuring tools
  32. Editing attributes
  33. Reprojecting and converting vector and raster data
  34. Joining tabular data
  35. Using temporary scratch layers
  36. Checking for topological errors and fixing them
  37. Adding data to spatial databases
  38. Summary
  39. 4. Spatial Analysis
  40. Combining raster and vector data
  41. Vector and raster analysis with Processing
  42. Leveraging the power of spatial databases
  43. Summary
  44. 5. Creating Great Maps
  45. Labeling
  46. Designing print maps
  47. Presenting your maps online
  48. Summary
  49. 6. Extending QGIS with Python
  50. Getting to know the Python Console
  51. Creating custom geoprocessing scripts using Python
  52. Developing your first plugin
  53. Summary
  54. 2. Module 2
  55. 1. Exploring Places – from Concept to Interface
  56. Acquiring data for geospatial applications
  57. Visualizing GIS data
  58. The basemap
  59. Summary
  60. 2. Identifying the Best Places
  61. Raster analysis
  62. Publishing the results as a web application
  63. Summary
  64. 3. Discovering Physical Relationships
  65. Spatial join for a performant operational layer interaction
  66. The CartoDB platform
  67. Leaflet and an external API: CartoDB SQL
  68. Summary
  69. 4. Finding the Best Way to Get There
  70. OpenStreetMap data for topology
  71. Database importing and topological relationships
  72. Creating the travel time isochron polygons
  73. Generating the shortest paths for all students
  74. Web applications – creating safe corridors
  75. Summary
  76. 5. Demonstrating Change
  77. TopoJSON
  78. The D3 data visualization library
  79. Summary
  80. 6. Estimating Unknown Values
  81. Interpolated model values
  82. A dynamic web application – OpenLayers AJAX with Python and SpatiaLite
  83. Summary
  84. 7. Mapping for Enterprises and Communities
  85. The cartographic rendering of geospatial data – MBTiles and UTFGrid
  86. Interacting with Mapbox services
  87. Putting it all together
  88. Going further – local MBTiles hosting with TileStream
  89. Summary
  90. 3. Module 3
  91. 1. Data Input and Output
  92. Finding geospatial data on your computer
  93. Describing data sources
  94. Importing data from text files
  95. Importing KML/KMZ files
  96. Importing DXF/DWG files
  97. Opening a NetCDF file
  98. Saving a vector layer
  99. Saving a raster layer
  100. Reprojecting a layer
  101. Batch format conversion
  102. Batch reprojection
  103. Loading vector layers into SpatiaLite
  104. Loading vector layers into PostGIS
  105. 2. Data Management
  106. Joining layer data
  107. Cleaning up the attribute table
  108. Configuring relations
  109. Joining tables in databases
  110. Creating views in SpatiaLite
  111. Creating views in PostGIS
  112. Creating spatial indexes
  113. Georeferencing rasters
  114. Georeferencing vector layers
  115. Creating raster overviews (pyramids)
  116. Building virtual rasters (catalogs)
  117. 3. Common Data Preprocessing Steps
  118. Converting points to lines to polygons and back – QGIS
  119. Converting points to lines to polygons and back – SpatiaLite
  120. Converting points to lines to polygons and back – PostGIS
  121. Cropping rasters
  122. Clipping vectors
  123. Extracting vectors
  124. Converting rasters to vectors
  125. Converting vectors to rasters
  126. Building DateTime strings
  127. Geotagging photos
  128. 4. Data Exploration
  129. Listing unique values in a column
  130. Exploring numeric value distribution in a column
  131. Exploring spatiotemporal vector data using Time Manager
  132. Creating animations using Time Manager
  133. Designing time-dependent styles
  134. Loading BaseMaps with the QuickMapServices plugin
  135. Loading BaseMaps with the OpenLayers plugin
  136. Viewing geotagged photos
  137. 5. Classic Vector Analysis
  138. Selecting optimum sites
  139. Dasymetric mapping
  140. Calculating regional statistics
  141. Estimating density heatmaps
  142. Estimating values based on samples
  143. 6. Network Analysis
  144. Creating a simple routing network
  145. Calculating the shortest paths using the Road graph plugin
  146. Routing with one-way streets in the Road graph plugin
  147. Calculating the shortest paths with the QGIS network analysis library
  148. Routing point sequences
  149. Automating multiple route computation using batch processing
  150. Matching points to the nearest line
  151. Creating a routing network for pgRouting
  152. Visualizing the pgRouting results in QGIS
  153. Using the pgRoutingLayer plugin for convenience
  154. Getting network data from the OSM
  155. 7. Raster Analysis I
  156. Using the raster calculator
  157. Preparing elevation data
  158. Calculating a slope
  159. Calculating a hillshade layer
  160. Analyzing hydrology
  161. Calculating a topographic index
  162. Automating analysis tasks using the graphical modeler
  163. 8. Raster Analysis II
  164. Calculating NDVI
  165. Handling null values
  166. Setting extents with masks
  167. Sampling a raster layer
  168. Visualizing multispectral layers
  169. Modifying and reclassifying values in raster layers
  170. Performing supervised classification of raster layers
  171. 9. QGIS and the Web
  172. Using web services
  173. Using WFS and WFS-T
  174. Searching CSW
  175. Using WMS and WMS Tiles
  176. Using WCS
  177. Using GDAL
  178. Serving web maps with the QGIS server
  179. Scale-dependent rendering
  180. Hooking up web clients
  181. Managing GeoServer from QGIS
  182. 10. Cartography Tips
  183. Using Rule Based Rendering
  184. Handling transparencies
  185. Understanding the feature and layer blending modes
  186. Saving and loading styles
  187. Configuring data-defined labels
  188. Creating custom SVG graphics
  189. Making pretty graticules in any projection
  190. Making useful graticules in printed maps
  191. Creating a map series using Atlas
  192. 11. Extending QGIS
  193. Defining custom projections
  194. Working near the dateline
  195. Working offline
  196. Using the QspatiaLite plugin
  197. Adding plugins with Python dependencies
  198. Using the Python console
  199. Writing Processing algorithms
  200. Writing QGIS plugins
  201. Using external tools
  202. 12. Up and Coming
  203. Preparing LiDAR data
  204. Opening File Geodatabases with the OpenFileGDB driver
  205. Using Geopackages
  206. The PostGIS Topology Editor plugin
  207. The Topology Checker plugin
  208. GRASS Topology tools
  209. Hunting for bugs
  210. Reporting bugs
  211. Bibliography
  212. Index

Designing print maps

In QGIS, print maps are designed in the print composer. A QGIS project can contain multiple composers, so it makes sense to pick descriptive names. Composers are saved automatically whenever we save the project. To see a list of all the compositions available in a project, go to Project | Composer Manager.

We can open a new composer by going to Project | New Print Composer or using Ctrl + P. The composer window consists of the following:

  • A preview area for the map composition displaying a blank page when a new composer is created
  • Panels for configuring Composition, Item properties, and Atlas generation, as well as a Command history panel for quick undo and redo actions
  • Toolbars to manage, save, and export compositions; navigate in the preview area; as well as add and arrange different composer items

Once you have designed your print map the way you want it, you can save the template to a composer template .qpt file by going to Composer | Save as template and reuse it in other projects by going to Composer | Add Items from Template.

Creating a basic map

In this example, we will create a basic map with a scalebar, a north arrow, some explanatory text, and a legend.

When we start the print composer, we first see the Composition panel on the right-hand side. This panel gives us access to paper options such as size, orientation, and number of pages. It is also the place to configure snapping behavior and output resolution.

First, we add a map item to the paper using the Add new map button, or by going to Layout | Add Map and drawing the map rectangle on the paper. Click on the paper, keep the mouse button pressed down, and drag the rectangle open. We can move and resize the map using the mouse and the Select/Move item tools. Alternatively, it is possible to configure all the map settings in the Item properties panel.

The Item properties panel's content depends on the currently selected composition item. If a map item is selected, we can adjust the map's Scale and Extents as well as the Position and size tool of the map item itself. At a Scale of 10,000,000 (with the CRS set to EPSG:2964), we can more or less fit a map of Alaska on an A4-size paper, as shown in the following screenshot. To move the area that is displayed within the map item and change the map scale, we can use the Move item content tool.

Creating a basic map

Adding a scalebar

After the map looks like what we want it to, we can add a scalebar using the Add new scalebar button or by going to Layout | Add Scalebar and clicking on the map. The Item properties panel now displays the scalebar's properties, which are similar to what you can see in the next screenshot. Since we can add multiple map items to one composition, it is important to specify which map the scale belongs to. The second main property is the scalebar style, which allows us to choose between different scalebar types, or a Numeric type for a simple textual representation, such as 1:10,000,000. Using the Units properties, we can convert the map units in feet or meters to something more manageable, such as miles or kilometers. The Segments properties control the number of segments and the size of a single segment in the scalebar. Further, the properties control the scalebar's color, font, background, and so on.

Adding a scalebar

Adding a North arrow image

North arrows can be added to a composition using the Add Image button or by going to Layout | Add image and clicking on the paper. To use one of the SVGs that are part of the QGIS installation, open the Search directories section in the Item properties panel. It might take a while for QGIS to load the previews of the images in the SVG folder. You can pick a North arrow from the list of images or select your own image by clicking on the button next to the Image source input. More map decorations, such as arrows or rectangle, triangle, and ellipse shapes can be added using the appropriate toolbar buttons: Add Arrow, Add Rectangle, and so on.

Adding a North arrow image

Adding a legend

Legends are another vital map element. We can use the Add new legend button or go to Layout | Add legend to add a default legend with entries for all currently visible map layers. Legend entries can be reorganized (sorted or added to groups), edited, and removed from the legend items' properties. Using the Wrap text on option, we can split long labels on multiple rows. The following screenshot shows the context menu that allows us to change the style (Hidden, Group, or Subgroup) of an entry. The corresponding font, size, and color are configurable in the Fonts section.

Additionally, the legend in this example is divided into three Columns, as you can see in the bottom-right section of the following screenshot. By default, QGIS tries to keep all entries of one layer in a single column, but we can override this behavior by enabling Split layers.

Adding a legend

Adding explanatory text to the map

To add text to the map, we can use the Add new label button or go to Layout | Add label. Simple labels display all text using the same font. By enabling Render as HTML, we can create more elaborate labels with headers, lists, different colors, and highlights in bold or italics using normal HTML notation. Here is an example:

<h1>Alaska</h1>
<p>The name <i>"Alaska"</i> means "the mainland".</p>
<ul><li>one list entry</li><li>another entry</li></ul>
<p style="font-size:70%;">[% format_date( $now ,'yyyy-mm-dd')%]</p>

Labels can also contain expressions such as these:

  • [% $now %]: This expression inserts the current timestamp, which can be formatted using the format_date function, as shown in the following screenshot
  • [% $page %] of [% $numpages %]: This expression can be used to insert page numbers in compositions with multiple pages
    Adding explanatory text to the map

Adding map grids and frames

Other common features of maps are grids and frames. Every map item can have one or more grids. Click on the + button in the Grids section to add a grid. The Interval and Offset values have to be specified in map units. We can choose between the following Grid types:

  • A normal Solid grid with customizable lines
  • Crosses at specified intervals with customizable styles
  • Customizable Markers at specified intervals
  • Frame and annotation only will hide the grid while still displaying the frame and coordinate annotations

For Grid frame, we can select from the following Frame styles:

  • Zebra, with customizable line and fill colors, as shown in the following screenshot
  • Interior ticks, Exterior ticks, or Interior and exterior ticks for tick marks pointing inside the map, outside it, or in both directions
  • Line border for a simple line frame

Using Draw coordinates, we can label the grid with the corresponding coordinates. The labels can be aligned horizontally or vertically and placed inside or outside the frame, as shown here:

Adding map grids and frames

Creating overview maps

Maps that show an area close up are often accompanied by a second map that tells the reader where the area is located in a larger context. To create such an overview map, we add a second map item and an overview by clicking on the + button in the Overviews section. By setting the Map frame, we can define which detail map's extent should be highlighted. By clicking on the + button again, we can add more map frames to the overview map. The following screenshot shows an example with two detail maps both of which are added to an overview map. To distinguish between the two maps, the overview highlights are color-coded (by changing the overview Frame style) to match the colors of the frames of the detail maps.

Creating overview maps

Tip

Every map item in a composition can display a different combination of layers. Generally, map items in a composer are synced with the map in the main QGIS window. So, if we turn a layer off in the main window, it is removed from the print composer map as well. However, we can stop this automatic synchronization by enabling Lock layers for a map item in the map item's properties.

Adding more details with attribute tables and HTML frames

To insert additional details into the map, the composer also offers the possibility of adding an attribute table to the composition using the Add attribute table button or by going to Layout | Add attribute table. By enabling Show only features visible within a map, we can filter the table and display only the relevant results. Additional filter expressions can be set using the Filter with option. Sorting (by name for example, as shown in the following screenshot) and renaming of columns is possible via the Attributes button. To customize the header row with bold and centered text, go to the Fonts and text styling section and change the Table heading settings.

Adding more details with attribute tables and HTML frames

Even more advanced content can be added using the Add html frame button. We can point the item's URL reference to any HTML page on our local machines or online, and the content (text and images as displayed in a web browser) will be displayed on the composer page.

Creating a map series using the Atlas feature

With the print composer's Atlas feature, we can create a series of maps using one print composition. The tool will create one output (which can be image files, PDFs, or multiple pages in one PDF) for every feature in the so-called Coverage layer.

Atlas can control and update multiple map items within one composition. To enable Atlas for a map item, we have to enable the Controlled by atlas option in the Item properties of the map item. When we use the Fixed scale option in the Controlled by atlas section, all maps will be rendered using the same scale. If we need a more flexible output, we can switch to the Margin around feature option instead, which zooms to every Coverage layer feature and renders it in addition to the specified margin surrounding area.

Creating a map series using the Atlas feature

To finish the configuration, we switch to the Atlas generation panel. As mentioned before, Atlas will create one map for every feature in the layer configured in the Coverage layer dropdown. Features in the coverage layer can be displayed like regular features or hidden by enabling Hidden coverage layer. Adding an expression to the Feature filtering option or enabling the Sort by option makes it possible to further fine-tune the results. The Output field can be one image or PDF for each coverage layer feature, or you can create a multipage PDF by enabling Single file export when possible before going to Composer | Export as PDF.

Once these configurations are finished, we can preview the map series by enabling the Preview Atlas button, which you can see in the top-left corner of the following screenshot. The arrow buttons next to the preview button are used to navigate between the Atlas maps.

Creating a map series using the Atlas feature