Book Image

QGIS Python Programming Cookbook, Second Edition - Second Edition

By : Joel Lawhead
Book Image

QGIS Python Programming Cookbook, Second Edition - Second Edition

By: Joel Lawhead

Overview of this book

QGIS is a desktop geographic information system that facilitates data viewing, editing, and analysis. Paired with the most efficient scripting language—Python, we can write effective scripts that extend the core functionality of QGIS. Based on version QGIS 2.18, this book will teach you how to write Python code that works with spatial data to automate geoprocessing tasks in QGIS. It will cover topics such as querying and editing vector data and using raster data. You will also learn to create, edit, and optimize a vector layer for faster queries, reproject a vector layer, reduce the number of vertices in a vector layer without losing critical data, and convert a raster to a vector. Following this, you will work through recipes that will help you compose static maps, create heavily customized maps, and add specialized labels and annotations. As well as this, we’ll also share a few tips and tricks based on different aspects of QGIS.
Table of Contents (16 chapters)
QGIS Python Programming Cookbook - Second Edition
About the Author
About the Reviewer
Customer Feedback

Creating an elevation hillshade

A hillshade, or shaded relief, is a technique to visualize elevation data in order to make it photorealistic for presentation as a map. This capability is part of GDAL and is available in QGIS in two different ways. It is a tool in the Terrain Analysis menu under the Raster menu, and it is also an algorithm in the Processing Toolbox.

Getting ready

You will need to download a Digital Elevation Model (DEM) from

Unzip the file named dem.asc and place it in your /qgis_data/rasters directory. A DEM is a 3D representation of a terrain's surface.

How to do it...

In this recipe, we will load the DEM layer and run the Hillshade processing algorithm against it. To do this, we need to perform the following steps:

  1. Start QGIS.

  2. From the Plugins menu, select Python Console.

  3. Import the processing module:

            import processing 
  4. Load and validate the layer:

            rasterLyr = QgsRasterLayer("/qgis_data/rasters/dem.asc...