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

Using generators for layer queries

Python generators provide an efficient way to process large datasets. A QGIS developer named Nathan Woodrow created a simple Python QGIS query engine, which uses generators to make fetching features from QGIS layers easier. We'll use this engine in this recipe to query a layer.

Getting ready

You need to install the query engine using easy_install or by downloading it and adding it to your QGIS Python installation. To use easy_install, run the following command from a console, which downloads a clone of the original code but includes a Python setup file:


You can also download the ZIP file from the following URL and copy the contents to your working directory or the site-packages directory of your QGIS Python installation:

You will also need to download the following zipped shapefile and decompress it to a directory...