Choropleth Map

Source: http://oliverobrien.co.uk/2009/08/openstreetmap-road-coverage-in-england/

Direct link to map: http://www.reedhome.org.uk/Documents/OSMCover.png

Choropleth maps display different statistical values for a variable in different colors or patterns. This map compares the Department of Transport measured road lengths by English county, and comparing them with the total lengths of roads in OpenStreetMap.