Flow Map

http://www.spokanestreetdepartment.org/flowmaps.htm

This is an example of a Flow map. Specifically this is a traffic flow map of the city of Spokane, Washington. The flow map shows linear movement between places, and the width of the lines is proportional to the quantity of traffic. Colors also distinguish between the road type. Interstates are shaded in grey and are the widest lines, followed by the black lines of the highways.