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

Iterating over layers

For many GIS operations, you need to loop through the map layers to look for specific information or to apply a change to all the layers. In this recipe, we'll loop through the layers and get information about them.

Getting ready

We'll need two layers in the same map projection to perform this recipe. You can download the first layer as a ZIP file from

You can download the second zipped layer from

Unzip both of these layers into a directory named ms within your qgis_data directory.

How to do it...

We will add the layers to the map through the map registry. Then, we will iterate through the map layers and print each layer's title. To do this, perform the following steps:

  1. First, let's open the polygon and the point layer using Python Console:

            lyr_1 = QgsVectorLayer("/qgis_data/ms/mississippi.shp",