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

Computing road slope using elevation data

A common geospatial workflow is to assign raster values to a coincident vector layer so that you can style or perform further analysis on the vector layer. This recipe will use this concept to illustrate the steepness of a road using color by mapping values to the road vector from a slope raster.

Getting ready

You will need to download a zipped directory from and place the directory, named road, in your qgis_data directory.

You must also have a verison of QGIS which includes GRASS and SAGA. For more information, see the Installing QGIS for development recipe from Chapter 1Automating QGIS,

How to do it...

We'll start with a DEM and compute its slope. Then, we'll load a road vector layer and break it into interval lengths of 500 meters. Next, we'll load the layer and style it using green, yellow, and red values for each segment to show the range of steepness. We'll overlay this layer on a hillshade...