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 vector layer in memory

Sometimes you need to create a temporary dataset for a quick output, or as an intermediate step in a more complex operation without the overhead of actually writing a file to disk. PyQGIS employs memory layers that allow you to create a complete vector dataset, including the geometry, fields, and attributes, virtually. Once the memory layer is created, you can work with it the same way you would with a vector layer loaded from the disk.

Getting ready

This recipe runs entirely inside the PyQGIS console, so no preparation or outside resources are required.

How to do it...

We will create a point vector layer with a few fields named Layer 1 and then validate it:

  1. Start QGIS.

  2. From the Plugins menu select Python Console.

  3. In the Python console, create a QgsVectorLayer, including fields, and specify it as type memory:

            vectorLyr = QgsVectorLayer('Point?crs=epsg:4326