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

Chapter 2. Viewing Spatial Data

In this chapter, we will cover how to view spatial data from different data sources. QGIS supports many file and database formats as well as standardized Open Geospatial Consortium (OGC) Web Services. We will first cover how we can load layers from these different data sources. We will then look into the basics of styling both vector and raster layers and will create our first map, which you can see in the following screenshot:

Viewing Spatial Data

We will finish this chapter with an example of loading background maps from online services.

Note

For the examples in this chapter, we will use the sample data provided by the QGIS project, which is available for download from http://qgis.org/downloads/data/qgis_sample_data.zip (21 MB). Download and unzip it.

Loading vector data from files

In this section, we will talk about loading vector data from GIS file formats, such as shapefiles, as well as from text files.

We can load vector files by going to Layer | Add Layer | Add Vector Layer and also using the Add Vector Layer toolbar button. If you like shortcuts, use Ctrl + Shift + V. In the Add vector layer dialog, which is shown in the following screenshot, we find a drop-down list that allows us to specify the encoding of the input file. This option is important if we are dealing with files that contain special characters, such as German umlauts or letters from alphabets different from the default Latin ones.

Loading vector data from files

What we are most interested in now is the Browse button, which opens the file-opening dialog. Note the file type filter drop-down list in the bottom-right corner of the dialog. We can open it to see a list of supported vector file types. This filter is useful to find specific files faster by hiding all the files of a different type, but be aware that the filter settings are stored and will be applied again the next time you open the file opening dialog. This can be a source of confusion if you try to find a different file later and it happens to be hidden by the filter, so remember to check the filter settings if you are having trouble locating a file.

We can load more than one file in one go by selecting multiple files at once (holding down Ctrl on Windows/Ubuntu or cmd on Mac). Let's give it a try:

  1. First, we select alaska.shp and airports.shp from the shapefiles sample data folder.
  2. Next, we confirm our selection by clicking on Open, and we are taken back to the Add vector layer dialog.
  3. After we've clicked on Open once more, the selected files are loaded. You will notice that each vector layer is displayed in a random color, which is most likely different from the color that you see in the following screenshot. Don't worry about this now; we'll deal with layer styles later in this chapter.
    Loading vector data from files

Even without us using any spatial analysis tools, these simple steps of visualizing spatial datasets enable us to find, for example, the southernmost airport on the Alaskan mainland.

Tip

There are multiple tricks that make loading data even faster; for example, you can simply drag and drop files from the operating system's file browser into QGIS.

Another way to quickly access your spatial data is by using QGIS's built-in file browser. If you have set up QGIS as shown in Chapter 1, Getting Started with QGIS, you'll find the browser on the left-hand side, just below the layer list. Navigate to your data folder, and you can again drag and drop files from the browser to the map.

Additionally, you can mark a folder as favorite by right-clicking on it and selecting Add as a favorite. In this way, you can access your data folders even faster, because they are added in the Favorites section right at the top of the browser list.

Another popular source of spatial data is delimited text (CSV) files. QGIS can load CSV files using the Add Delimited Text Layer option available via the menu entry by going to Layer | Add Layer | Add Delimited Text Layer or the corresponding toolbar button. Click on Browse and select elevp.csv from the sample data. CSV files come with all kinds of delimiters. As you can see in the following screenshot, the plugin lets you choose from the most common ones (Comma, Tab, and so on), but you can also specify any other plain or regular-expression delimiter:

Loading vector data from files

If your CSV file contains quotation marks such as, " or ', you can use the Quote option to have them removed. The Number of header lines to discard option allows us to skip any potential extra lines at the beginning of the text file. The following Field options include functionality for trimming extra spaces from field values or redefine the decimal separator to a comma. The spatial information itself can be provided either in the two columns that contain the coordinates of points X and Y, or using the Well known text (WKT) format. A WKT field can contain points, lines, or polygons. For example, a point can be specified as POINT (30 10), a simple line with three nodes would be LINESTRING (30 10, 10 30, 40 40), and a polygon with four nodes would be POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10)).

Note

Note that the first and last coordinate pair in a polygon has to be identical.

WKT is a very useful and flexible format. If you are unfamiliar with the concept, you can find a detailed introduction with examples at http://en.wikipedia.org/wiki/Well-known_text.

After we've clicked on OK, QGIS will prompt us to specify the layer's coordinate reference system (CRS). We will talk about handling CRS next.