Rendering map layers based on rules

Rendering rules provide a powerful way to control how and when a layer is displayed relative to other layers or properties of the layer itself. This recipe demonstrates how to use a rule-based renderer to color code a layer based on an attribute.

Getting ready

You will need to download a zipped shapefile from the following URL:

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

Unzip it and place it in directory named ms in your qgis_data directory.

In that same directory, download and unzip the following shapefile:

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

Finally, add this shapefile to the directory as well:

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

How to do it...

We will set up a railroad layer; then, we'll set up our rules as Python tuples to color code it, based on frequency of use. Finally, we'll add some other layers to the map for reference.

1. First, we need the QtGui library to work...