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
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface

Creating a map bookmark


Map bookmarks allow you to save a location on a map in QGIS, so you can quickly jump to the points you need to view repeatedly without manually panning and zooming the map. PyQGIS does not contain API commands to read, write, and zoom to bookmarks. Fortunately, QGIS stores the bookmarks in an SQLite database. Python has a built-in SQLite library that we can use to manipulate bookmarks using the database API.

Getting ready

You can download a census tract polygon shapefile to use with this recipe from https://github.com/GeospatialPython/Learn/raw/master/GIS_CensusTract.zip.

Extract it to your qgis_data directory. We are going to create a bookmark that uses an area of interest within this shapefile. So, you can manually load the bookmark in order to test it out.

How to do it...

We will access the QGIS configuration variables to get the path of the user database, which stores the bookmarks. Then, we'll connect to this database and execute an SQL query that inserts a bookmark...