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

Reprojecting a vector layer

Reprojecting a vector layer is inherent to QGIS; however, to access it from Python, we must use the Processing Toolbox.

Getting ready

For this recipe, we'll need the Mississippi cities shapefile in the Mississippi Transverse Mercator Projection, which can be downloaded as a ZIP file here:

Extract the zipped shapefile to a directory named /qgis_data/ms.

How to do it...

To reproject the layer, we'll simply call the qgis:reprojectlayer processing algorithm specifying the input shapefile, the new projection, and the output file name.

  1. Start QGIS.

  2. From the Plugins menu, select Python Console.

  3. First, we need to import the processing module:

            import processing 
  4. Next, we run the reprojection algorithm: