QGIS Python Programming Cookbook - Second Edition

Performing a union on vector shapes

A union turns two overlapping shapes into one. This task can be easily accomplished with the Processing Toolbox. In this recipe, we'll merge the outline of a covered building to the footprint of the main building.

Getting ready

You can download the building files from the following URL and extract them to a directory named /qgis_data/union:

https://github.com/GeospatialPython/Learn/raw/master/union.zip

How to do it...

All we need to do is run the qgis:union algorithm:

1. Start QGIS.
2. From the Plugins menu, select Python Console.
3. Import the processing module:

           import processing 
   

4. Now, run the algorithm specifying the two input shapes and the single output file:

    processing.runandload("qgis:union", "/qgis_data/union/building.shp", ...