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

Using null symbols

Null symbols are a tool that allow you to have a layer without any symbology. Layers without symbology can be useful when you don't need to see a layer but need to interact with it in other ways, such as querying or specialized labeling. For example, if you have an imagery basemap, you may want to have labels on the map but no features. In this recipe, we'll load a point layer and label it, but use null symbology.

Getting ready

Download the zipped shapefile from

Extract the shapefile to a directory named ms in your qgis_data directory.

How to do it...

We will load the layer, set the renderer to the null symbol renderer, set up our labeling configuration, and then add it to the map. This recipe builds on the previous labeling recipe:

  1. First, to save space, we'll specify the path to the shapefile:

            src = "/qgis_data/ms/MSCities_Geo_Pts.shp" 
  2. Next, we'll load the layer:

            lyr = QgsVectorLayer...