book

QGIS: Becoming a GIS Power User

Name: QGIS: Becoming a GIS Power User
ISBN: 9781788299725

by Anita Graser, Ben Mearns, Alex Mandel, Víctor Olaya Ferrero, Alexander Bruy

February 2017

Beginner to intermediate

819 pages

17h 52m

English

Packt Publishing

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QGIS: Becoming a GIS Power User
Table of Contents
QGIS: Becoming a GIS Power User
QGIS: Becoming a GIS Power User
Credits
Preface
What this learning path covers
What you need for this learning path
Who this learning path is for
Reader feedback
Customer support
Downloading the example codeErrataPiracyQuestions

1. Module 1
1. Getting Started with QGIS
Installing QGISInstalling QGIS on WindowsInstalling on Ubuntu
Running QGIS for the first time
Introducing the QGIS user interface
Finding help and reporting issues
Summary
2. Viewing Spatial Data
Loading vector data from files
Dealing with coordinate reference systems
Loading raster files
Georeferencing raster maps
Loading data from databases
Loading data from OGC web services
Styling raster layers
Styling vector layers
Creating point styles – an example of an airport styleCreating line styles – an example of river or road stylesCreating polygon styles – an example of a landmass style
Loading background maps
Dealing with project files
Summary
3. Data Creation and Editing
Creating new vector layers
Working with feature selection tools
Selecting features with the mouseSelecting features with expressionsSelecting features using spatial queries
Editing vector geometries
Using basic digitizing toolsUsing advanced digitizing toolsUsing snapping to enable topologically correct editing
Using measuring tools
Editing attributes
Editing attributes in the attribute tableEditing attributes in the feature formCreating a feature form using autogenerateDesigning a feature form using drag and drop designerDesigning a feature form using a .ui fileCalculating new attribute values
Reprojecting and converting vector and raster data
Joining tabular data
Setting up a join in Layer PropertiesChecking join results in the attribute table
Using temporary scratch layers
Checking for topological errors and fixing them
Finding errors with the Topology CheckerFixing invalid geometry errors
Adding data to spatial databases
Summary
4. Spatial Analysis
Analyzing raster dataClipping rastersAnalyzing elevation/terrain dataUsing the raster calculator
Combining raster and vector data
Converting between rasters and vectorsAccessing raster and vector layer statisticsComputing zonal statisticsCreating a heatmap from points
Vector and raster analysis with Processing
Finding nearest neighborsConverting between points, lines, and polygonsIdentifying features in the proximity of other featuresSampling a raster at point locationsMapping density with hexagonal gridsCalculating area shares within a regionBatch-processing multiple datasetsAutomated geoprocessing with the graphical modelerDocumenting and sharing models
Leveraging the power of spatial databases
Selecting by location in SpatiaLiteAggregating data in SpatiaLite
Summary
5. Creating Great Maps
Advanced vector stylingCreating a graduated styleCreating and using color rampsUsing categorized styles for nominal dataCreating a rule-based style for road layersCreating data-defined symbologyCreating a dynamic heatmap styleCreating a 2.5D styleAdding live layer effectsWorking with different styles
Labeling
Customizing label text stylesControlling label formattingConfiguring label buffers, background, and shadowsControlling label placementConfiguring point labelsConfiguring line labelsConfiguring polygon labelsPlacing labels manuallyControlling label rendering
Designing print maps
Creating a basic mapAdding a scalebarAdding a North arrow imageAdding a legendAdding explanatory text to the mapAdding map grids and framesCreating overview mapsAdding more details with attribute tables and HTML framesCreating a map series using the Atlas feature
Presenting your maps online
Exporting a web mapCreating map tilesExporting a 3D web map
Summary
6. Extending QGIS with Python
Adding functionality using actionsConfiguring your first Python actionOpening files using actionsOpening a web browser using actions
Getting to know the Python Console
Loading and exploring datasetsStyling layersFiltering dataCreating a memory layerExporting map images
Creating custom geoprocessing scripts using Python
Writing your first Processing scriptWriting a script with vector layer outputVisualizing the script progress
Developing your first plugin
Creating the plugin template with Plugin BuilderCustomizing the plugin GUIImplementing plugin functionalityCreating a custom map tool
Summary
2. Module 2
1. Exploring Places – from Concept to Interface
The development community and dependenciesData format read/writeGeospatial coordinate transformationAnalysisWeb publishingInstallationLinuxMacWindowsOSGeo-Live
Acquiring data for geospatial applications
Producing geospatial data with georeferencingTable joinGeocodeOrthorectifyThe spatial reference manipulation – making the coordinates line upSetting CRSTransformation and projection
Visualizing GIS data
The layer styleLabels
The basemap
Using OpenStreetMap for the basemap dataAvoiding obscurity and confusionThe layer scale dependencyThe label conflictThe polygon label conflict resolutionTile cachesGenerating and testing a simple directory-based tile cache structureCreate a layer description file for the TileLayer plugin
Summary
2. Identifying the Best Places
Vector data – Extract, Transform, and LoadLoading data and establishing the CRS conformityThe extracting (filtering) featuresConverting to rasterDoing more at once—working in batch
Raster analysis
Map algebraAdditive modelingProximityCreating a proximity to the easements gridSlopeCombining the criteria with Map CalculatorZonal statistics
Publishing the results as a web application
qgis2leaf
Summary
3. Discovering Physical Relationships
Hydrological modelingPreparing the dataFilling the grid sinksClipping the grid to study the area by mask layerModeling the hydrological network based on elevationWorkflow automation with the graphical modelsCreating a graphical modelAdding the input parametersAdding the raster parameter – elevationAdding the vector parameter – extentAdding the algorithmsFill SinksClip rasterChannel network and drainage basinsRunning the model
Spatial join for a performant operational layer interaction
The NNJoin plugin
The CartoDB platform
Publishing the data to CartoDBPreparing a CartoDB SQL QueryGenerating the test dataThe CartoDB SQL view tabThe QGIS CartoDB pluginThe CartoDB SQL API
Leaflet and an external API: CartoDB SQL
Summary
4. Finding the Best Way to Get There
Postgres with PostGIS and pgRoutingInstalling Postgres/PostGIS/pgRoutingCreating a new Postgres databaseRegistering the PostGIS and pgRouting extensions
OpenStreetMap data for topology
Downloading the OSM dataAdding the data to the mapProjecting the OSM dataSplitting all the lines at intersections
Database importing and topological relationships
Connecting to the databaseImporting into PostGIS with DB ManagerCreating the topological network dataAn alternate workflow: topology with osm2poUsing the pgRouting Layer plugin to test
Creating the travel time isochron polygons
Generating the travel time for each road segmentCreating isochron polygonsConverting the travel time lines to pointsSelecting the travel time ranges in points and creating convex hulls
Generating the shortest paths for all students
Finding the associated segment for a student locationCalculating the accumulated shortest paths by segmentFlow symbology
Web applications – creating safe corridors
Registering a Twitter account and API accessSetting up the Twitter Tools API
Summary
5. Demonstrating Change
Leveraging spatial relationshipsGathering the dataBoundariesTabular data from American FactFinderPreparing and exporting the dataThe tabular dataCombining it yearlyUpdating and removing fieldsThe boundary dataCalculating the average white population change in each census tractThe spatial join in SpatiaLiteCreating a SpatiaLite databaseImporting layers to SpatiaLiteQuerying and loading the SpatiaLite layer from the DB Manager
TopoJSON
An example of GeoJSONAn example of TopoJSONVector simplificationSimplification methodsOther optionsSimplifying for TopoJSONSimplifying for other outputsConverting to TopoJSONWeb mapshaperThe command-line tool
The D3 data visualization library
What is D3?Some fundamentalsParsingGraphic elements, SVG, path, and CanvasProjectionShape generatorScalesBindingSelect, Select All, Enter, Return, Exit, Insert, and AppendAnimated time series mapThe development environmentCodemain.jsOutput
Summary
6. Estimating Unknown Values
Importing the dataConnecting and importing from MySQL in QGISConverting to spatial formatThe layer/table relationsNetCDFViewing NetCDF in QGIS
Interpolated model values
Python for workflow automationKnowing your environmentGenerating the parameter grids for each time periodWhat this code doesRunning a code in PythonRunning the printed commands in the Windows command consoleThe subprocess moduleCalculating the vulnerability indexCreating regular pointsSampling the index grid by pointsCreate SQLite database and import
A dynamic web application – OpenLayers AJAX with Python and SpatiaLite
Server side – CGI in PythonPython CGI developmentStarting a CGI hostingTesting the CGI hostingDebugging server-side codeOur Python server-side, database-driven codePySpatiaLiteThe Python code for web access to SQLite through JSONThe OpenLayers/jQuery client-side codeExporting the OpenLayers 3 map using QGISModifying the exported OpenLayers 3 map applicationAdding an interactive HTML elementAJAX – the glue between frontend and backendAdding an AJAX call to the singleclick event handlerPopulating and triggering the popup from the callback functionTesting the application
Summary
7. Mapping for Enterprises and Communities
Google Sheets for data managementCreating a new Google documentPublishing Google Sheets on the WebPreviewing JSONParsing the JSON dataStarting up the serverTest parsing with jQueryRolloutAssigning permissions to additional usersThe editing workflowThe publishing workflowViewing the changes in your JSON feed
The cartographic rendering of geospatial data – MBTiles and UTFGrid
OpenStreetMap to SpatiaLiteTo tile and use UTFGrid with TileMillPreparing a basemap from OSMPreparing the operational layer in TileMillExporting MBTilesUploading to MapboxThe MBTiles file
Interacting with Mapbox services
Connecting your local app with a hosted serviceThe API tokenMapbox.jsSimple UTFGrid modificationPreviewing a simple UTFGrid modificationOpenLayersCode modification
Putting it all together
Parsing the sheets JSON feedCompleting the application
Going further – local MBTiles hosting with TileStream
Setting up a Vagrant virtual Linux instanceInstalling Node.js and TileStreamSetting up and starting TileStream
Summary
3. Module 3
1. Data Input and Output
Introduction
Finding geospatial data on your computer
Getting readyHow to do it…How it works…There's more…Adding layers with the Layer menuAdding a folder to FavoritesNonfile data sources
Describing data sources
Getting readyHow to do it…How it works…There's more…See also
Importing data from text files
How to do it…How it works…There's more…See also
Importing KML/KMZ files
How to do it…How it works…There's more…
Importing DXF/DWG files
How to do it…How it works…There's more…Opening DWG files
Opening a NetCDF file
How to do it…How it works…There's more…The NetCDF Browser plugin
Saving a vector layer
Getting readyHow to do it…How it works…There's more…Fine-tuning the export operationOpening the layer after creating it
Saving a raster layer
Getting readyHow to do it…How it works…There's more…
Reprojecting a layer
Getting readyHow to do it…How it works…There's more…
Batch format conversion
Getting readyHow to do it…How it works…There's more…
Batch reprojection
How to do it…How it works…There's more…
Loading vector layers into SpatiaLite
Getting readyHow to do it…How it works…There's more…See also
Loading vector layers into PostGIS
Getting readyHow to do it…How it works…There's more…See also
2. Data Management
Introduction
Joining layer data
Getting readyHow to do it…How it works…There's more…
Cleaning up the attribute table
Getting readyHow to do it…How it works…There's more…See also
Configuring relations
Getting readyHow to do it…How it works…
Joining tables in databases
Getting readyHow to do it…How it works…There's more…See also
Creating views in SpatiaLite
Getting readyHow to do it…How it works…There's more…See also
Creating views in PostGIS
Getting readyHow to do it…How it works…There's more…See also
Creating spatial indexes
Getting readyHow to do it…How it works…There's more…See also
Georeferencing rasters
Getting readyHow to do it…How it works…There's more…See also
Georeferencing vector layers
Getting readyHow to do it…How it works…There's more…See also
Creating raster overviews (pyramids)
Getting readyHow to do it…How it works…There's more…See also
Building virtual rasters (catalogs)
Getting readyHow to do it…How it works…There's more…See also
3. Common Data Preprocessing Steps
Introduction
Converting points to lines to polygons and back – QGIS
Getting readyHow to do it…Converting points to lines (or polygons)Converting lines to polygonsConverting polygons to linesConverting polygons or lines to pointsHow it works…There's more…
Converting points to lines to polygons and back – SpatiaLite
Getting readyHow to do it…Points to linesLines to polygonsHow it works…There's more…See also
Converting points to lines to polygons and back – PostGIS
Getting readyHow to do it…Converting points to linesConverting lines to polygonsConverting lines or polygons to pointsHow it works…There's more…See also
Cropping rasters
Getting readyHow to do it…How it works…There's more…See also
Clipping vectors
Getting readyHow to do it…How it works…There's more…See also
Extracting vectors
Getting readyHow to do it…How it works…There's more…See also
Converting rasters to vectors
Getting readyHow to do it…How it works…There's more…See also
Converting vectors to rasters
Getting readyHow to do it…How it works…There's more…See also
Building DateTime strings
Getting readyHow to do it…How it works…There's more…See also
Geotagging photos
Getting readyHow to do it…How it works…There's more…See also
4. Data Exploration
Introduction
Listing unique values in a column
Getting readyHow to do it…How it works…There's more…
Exploring numeric value distribution in a column
Getting readyHow to do it…How it works...See also
Exploring spatiotemporal vector data using Time Manager
Getting readyHow to do it…How it works…See also
Creating animations using Time Manager
Getting readyHow to do it…How it works…
Designing time-dependent styles
Getting readyHow to do it…How it works…See also
Loading BaseMaps with the QuickMapServices plugin
Getting readyHow to do it…How it works…There's more…See also
Loading BaseMaps with the OpenLayers plugin
Getting readyHow to do it…How it works…There's more…See also
Viewing geotagged photos
Getting readyHow to do it…Going a little furtherHow it works…There's more…See also
5. Classic Vector Analysis
Introduction
Selecting optimum sites
Getting readyHow to do it…How it works…There's more…
Dasymetric mapping
Getting readyHow to do it…How it works…
Calculating regional statistics
Getting readyHow to do it…How it works…
Estimating density heatmaps
Getting readyHow to do it…How it works…
Estimating values based on samples
Getting readyHow to do it…How it works…There's more…See also
6. Network Analysis
Introduction
Creating a simple routing network
Getting readyHow to do it…How it works…There's more…
Calculating the shortest paths using the Road graph plugin
Getting readyHow to do it…How it works…See also
Routing with one-way streets in the Road graph plugin
Getting readyHow to do it…How it works…
Calculating the shortest paths with the QGIS network analysis library
Getting readyHow to do it…How it works…See also
Routing point sequences
Getting readyHow to do it…How it works…There's more…See also
Automating multiple route computation using batch processing
Getting readyHow to do it…
Matching points to the nearest line
Getting readyHow to do it…How it works…
Creating a routing network for pgRouting
Getting readyHow to do it…How it works…See also
Visualizing the pgRouting results in QGIS
Getting readyHow to do it…How it works…See also
Using the pgRoutingLayer plugin for convenience
Getting readyHow to do it…How it works…See also
Getting network data from the OSM
Getting readyHow to do it…How it works…
7. Raster Analysis I
Introduction
Using the raster calculator
Getting readyHow to do it…How it works…There's more…See also
Preparing elevation data
Getting readyHow to do it…How it works…There's more…
Calculating a slope
Getting readyHow to do it…How it works…There's more…Using a ratio for elevation valuesOther slope algorithmsCalculating the slopeSee also
Calculating a hillshade layer
Getting readyHow to do it…How it works…There's more…Enhancing your map view with a hillshade layer
Analyzing hydrology
Getting readyHow to do it…How it works…There's more…
Calculating a topographic index
Getting readyHow to do it…How it works…There's more…
Automating analysis tasks using the graphical modeler
Getting readyHow to do it…How it works…See also
8. Raster Analysis II
Introduction
Calculating NDVI
Getting readyHow to do it…How it works…There's more…Extracting bands
Handling null values
How to do it…How it works…There's more…Controlling the rendering of null values
Setting extents with masks
How to do it…How it works…There's more…Restricting analysis to a given areaRemoving superfluous no-data valuesMasking using a vector mask
Sampling a raster layer
Getting readyHow to do it…How it works…There's more…Other raster-vector data transfer operations
Visualizing multispectral layers
Getting readyHow to do it…How it works…There's more…See also
Modifying and reclassifying values in raster layers
Getting readyHow to do it…How it works…There's more…Reclassifying into classes of equal amplitudeReclassifying into classes of equal areaSee also
Performing supervised classification of raster layers
Getting readyHow to do it…How it works…There's more…See also
9. QGIS and the Web
Introduction
Using web services
Getting readyHow to do it…How it works…There's more…See also
Using WFS and WFS-T
Getting readyHow to do it…How it works…There's more…
Searching CSW
Getting readyHow to do it…How it works…There's more…See also
Using WMS and WMS Tiles
Getting readyHow to do it…How it works…There's more…See also
Using WCS
Getting readyHow to do it…How it works…There's more…
Using GDAL
Getting readyHow to do it…How it works…There's more…See also
Serving web maps with the QGIS server
Getting readyHow to do it…How it works…There's more…See also
Scale-dependent rendering
Getting readyHow to do it…How it works…There's more…See also
Hooking up web clients
Getting readyHow to do it…How it works…There's more…See also
Managing GeoServer from QGIS
Getting readyHow to do it…How it works…There's more…Editing a remote styleSupport for multiple formatsSee also
10. Cartography Tips
Introduction
Using Rule Based Rendering
Getting readyHow to do it…How it works…There's more…
Handling transparencies
Getting readyHow to do it…How it works…There's more…
Understanding the feature and layer blending modes
Getting readyHow to do it…How it works…
Saving and loading styles
Getting readyHow to do it…How it works…There's more…
Configuring data-defined labels
Getting readyHow to do it…Example: moving and rotating a labelHow it works…There's more…
Creating custom SVG graphics
Getting readyHow to do it…How it works…There's more…See also
Making pretty graticules in any projection
Getting readyHow to do it…How it works…There's more…See also
Making useful graticules in printed maps
Getting readyHow to do it…How it works…There's more…
Creating a map series using Atlas
Getting readyHow to do it…How it works…There's more…
11. Extending QGIS
Introduction
Defining custom projections
Getting readyHow to do it…How it works…There's more…See also
Working near the dateline
Getting readyHow to do it…How it works…See also
Working offline
Getting readyHow to do it…How it works…There's more…See also
Using the QspatiaLite plugin
Getting readyHow to do it…How it works…There's more…See also
Adding plugins with Python dependencies
Getting readyHow to do it…How it works…There's more…
Using the Python console
Getting readyHow to do it…How it works…There's more…See also
Writing Processing algorithms
Getting readyHow to do it…How it works…There's more…See also
Writing QGIS plugins
Getting readyHow to do it…How it works…There's more…Creating plugins with more complex UI elementsDocumenting you pluginReleasing your plugin
Using external tools
Getting readyHow to do it…GPSBabelspatialite-guipgAdminHow it works…There's more…
12. Up and Coming
Introduction
Preparing LiDAR data
Getting readyHow to do it…How it works…There's more…
Opening File Geodatabases with the OpenFileGDB driver
Getting readyHow to do it…How it works…There's more…See also
Using Geopackages
Getting readyHow to do it…How it works…There's more…See also
The PostGIS Topology Editor plugin
Getting readyHow to do it…How it works…See also
The Topology Checker plugin
Getting readyHow to do it…How it works…See also
GRASS Topology tools
Getting readyHow to do it…How it works…There's more…See also
Hunting for bugs
Getting readyHow to do it…Creating a backtrace under LinuxCapturing debug output with DebugView under WindowsHow it works…There's more…See also
Reporting bugs
Getting readyHow to do it…How it works…There's more…See also
Bibliography
Index

Content preview from QGIS: Becoming a GIS Power User

Handling null values

Null values are a particular type of values that are used to indicate cells where the value for a given layer is not defined. Understanding how to use them is important to avoid wrong results when performing analyses but also to use them as a tool to get better and more correct results. This recipe explains some of the fundamental ideas about null values in raster layers.

How to do it…

The watershed.tif layer contains the area of a watershed. Cells inside the watershed are cells from which water will eventually flow into the outlet point of the watershed. The remaining cells belong to a different watershed. To mask the DEM with the watershed mask, follow these steps:

Open the watershed.tif layer.
Open the identify tool and check ...

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QGIS: Becoming a GIS Power User

by Anita Graser, Ben Mearns, Alex Mandel, Víctor Olaya Ferrero, Alexander Bruy

Handling null values

How to do it…

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