Each box on the map represents a /8 on the internet. E.g. 10 is 10.0.0.0/8. This checkerboard pattern is recursive; check 192.168.0.0 for an example.
Gratuitous XKCD link
This map is generated from three sources: RFC5735, IANA's current assignments and the latest BGP route views from the Route Views project. It is created using the Python Image Manipulation library.
© Colm MacCárthaigh 2010