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

Change map layer transparency

Map layer transparency allows you to change the opacity of a layer, so the items behind it are visible to some degree. A common technique is to make a vector layer polygon partially transparent in order to allow the underlying imagery or elevation data to add texture to the data.

Getting ready

In a directory called ms, in your qgis_data directory, download and extract the following shapefile from

How to do it...

The process is extremely simple. Transparency is just a method:

  1. First, we load the shapefile layer:

            lyr = QgsVectorLayer("/qgis_data/ms/mississippi.shp",
                                 "Mississippi", "ogr") 
  2. Next, we set the layer's transparency to 50 percent:

  3. Finally, we add this layer to the map:


How it works...

If you set the transparency to 100 percent, the layer is completely...