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
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface

Symbolizing a vector layer


The appearance of layers on a QGIS map is controlled by its symbology. A layer's symbology includes the renderer and one or more symbols. The renderer provides rules dictating the appearance of symbols. The symbols describe properties, including color, shape, size, and line width. In this recipe, we'll load a vector layer, change its symbology, and refresh the map.

Getting ready

Download the zipped shapefile and extract it to your qgis_data directory into a folder named ms from https://github.com/GeospatialPython/Learn/raw/master/Mississippi.zip

How to do it...

We will load a layer, add it to the map layer registry, change the layer's color, and then refresh the map. To do this, perform the following steps:

  1. First, using Python Console, we must import the QtGui library in order to access the QColor object, which is used to describe colors in the PyQGIS API:

            from PyQt4.QtGui import * 
    
  2. Next, we create our vector layer, as follows:

            lyr = QgsVectorLayer...