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 a categorized vector layer symbol

A categorized vector layer symbol allows you to create distinct categories with colors and labels for unique features. This approach is typically used for datasets with a limited number of unique types of features. In this recipe, we'll categorize a vector layer into three different categories.

Getting ready

For this recipe, we'll use a land use shapefile, which you can download from

Extract it to a directory named hancock in your qgis_data directory.

How to do it...

We will load the vector layer, create three categories of land use, and render them as categorized symbols. To do this, we need to perform the following steps:

  1. First, we need to import the QColor object for our category colors:

            from PyQt4.QtGui import QColor 
  2. Then, we load the vector layer:

            lyr = QgsVectorLayer("Users/joellawhead/qgis_data
                                  /hancock/landuse.shp", "Land...