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

Adding a line feature to a vector layer

Adding a line to a vector layer in QGIS is identical to adding a single point, but you just add more points to the QgsGeometry object.

Getting ready

For this recipe, you will need to download a zipped line shapefile containing two line features from the following URL:

Extract the ZIP file to a directory named paths in your /qgis_data directory.

How to do it...

We will load the line layer from the shapefile, build a list of points, create a new geometry object and add the points as a line, create a new feature, set the geometry, and add it to the layer's data provider. Finally, we will update the extents of the layer to make sure the bounding box of the layer encapsulates the new feature:

  1. Start QGIS.

  2. From the Plugins menu, select Python Console.

  3. First, we load the line layer and ensure it is valid: