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

Adding a polygon feature to a vector layer

In this recipe, we'll add a polygon to a layer. A polygon is the most complex kind of geometry; however, in QGIS the API is very similar to a line.

Getting ready

For this recipe, we'll use a simple polygon shapefile which you can download as a ZIP file from the following URL:

Extract this shapefile to a folder called polygon in your /qgis_data directory.

How to do it...

This recipe will follow the standard PyQGIS process of loading a layer, building a feature, and adding it to the layer's data provider:

  1. Start QGIS.

  2. From the Plugins menu, select Python Console.

  3. First, load the layer and validate it:

            vectorLyr=  QgsVectorLayer('/qgis_data/polygon/polygon.shp',
                                       'Polyon' , "ogr") 
  4. Next, access the layer's data provider:

            vpr = vectorLyr.dataProvider() 
  5. Now, we build a list of points for the polygon...