Each colour represents the approximate area of a postcode outcode. For example pink is BS8, blue is BS1. Each individual cell is the area covered by a full postcode, such as BS1 5TX. Darker colours indicate multiple postcodes at the exact same latlon (For example the council building has many postcodes and it the blue splodge on the centre left).
The areas are generated using the voronoi functions from toxiclibs.
Uploaded with Skitch. Contains Royal Mail data © Royal Mail copyright and database right 2011, Contains National Statistics data © Crown copyright and database right 2011.