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 alpha values to show data density

Thematic maps often use a color ramp based on a single color to show data density. Darker colors show higher concentration of objects, while lighter colors show lower concentrations. You can use a transparency ramp instead of a color ramp to show density as well. This technique is useful if you want to overlay the density layer on imagery or other vector layers. In this recipe, you use some bear-sighting data to show concentrations of bears over an area. We'll use alpha values to show the density. We'll use an unusual hexagon grid to divide the area and a rule-based renderer to build the display.

Getting ready

You will need to install the MMQGIS plugin used to build the hexagon grid using the QGIS plugin manager.

You also need to download the bear data from the following URL, unzip the shapefile, and put it in the ms directory of your qgis_data directory:

How to do it...

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