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

Measuring distance along a line

In this recipe, we'll measure the distance along a line with multiple vertices.

Getting ready

For this recipe, we'll use a line shapefile with two features. You can download the shapefile as a .zip file from

Unzip the shapefile into a directory named qgis_data/shapes within your root or home directory.

How to do it...

The steps for this recipe are fairly straightforward. We'll extract the geometry from the first line feature and pass it to the measurement object, as shown here:

  1. First, we must load the QGIS constants library:

            from qgis.core import QGis 
  2. Load the line layer:

            lyr = QgsVectorLayer("/qgis_data/shapes/paths.shp", "Route", "ogr") 
  3. Grab the features:

            fts = lyr.getFeatures() 
  4. Get the first feature:

            route = 
  5. Create the measurement object instance:

            d = QgsDistanceArea() 
  6. Then, we must configure the QgsDistanceArea object to...