Flow maps

Flow maps
http://infosthetics.com/archives/2007/02/cartographic_flow_map_layout.html

A flow map or flow chart like the one above demonstrate the connection between different pieces of information and "flow" in accordance to where they are on the map. Flow maps show the movement of different objects from one place to another.  A flow map also has the ability to show the process of something starting with the beginning and leading all the way towards the final process.