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 dynamic forms in QGIS

When you edit the fields of a layer in QGIS, you have the option of using a spreadsheet-like table view or a database-style form view. Forms are useful because you can change the design of the form, and you can add interactive features which react to user input to better control data editing. In this recipe, we'll add some custom validation to a form that checks user input for valid values.

Getting ready

You will need to download the following zipped shapefile and decompress it to a directory named ms in your qgis_data directory:

You'll also need to create a blank Python file called, which you'll edit with the following steps. Put the in the ms directory of your qgis_data directory with the shapefile.

How to do it...

We'll create the two functions we need for our validation engine. Then, we'll use the QGIS interface to attach the action to the layer. Make sure you add...