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
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Rendering map layers based on rules

Rendering rules provide a powerful way to control how and when a layer is displayed relative to other layers or properties of the layer itself. This recipe demonstrates how to use a rule-based renderer to color code a layer based on an attribute.

Getting ready

You will need to download a zipped shapefile from the following URL:

Unzip it and place it in directory named ms in your qgis_data directory.

In that same directory, download and unzip the following shapefile:

Finally, add this shapefile to the directory as well:

How to do it...

We will set up a railroad layer; then, we'll set up our rules as Python tuples to color code it, based on frequency of use. Finally, we'll add some other layers to the map for reference.

  1. First, we need the QtGui library to work...