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

Setting scale-based visibility for a layer

Sometimes, a GIS layer only makes sense when it is displayed at a certain scale, for example, a complex road network. PyQGIS supports scale-based visibility to programmatically set the scale range, in which a layer is displayed. In this recipe, we'll investigate scale-dependent layers.

Getting ready

You will need the sample census tract shapefile, available as a ZIP file from

Extract the zipped layer to a directory named census in your qgis_data directory.

How to do it...

We will load the vector layer, toggle scale-based visibility, set the visibility range, and then add the layer to the map. To do this, perform the following steps:

  1. First, we load the layer:

            lyr = QgsVectorLayer("/qgis_data/census/GIS_CensusTract_poly.shp",
                                 "Census", "ogr") 
  2. Next, we toggle scale-based visibility:

  3. Then...