Dot Distribution Map

Dot distribution maps are most commonly used to show population in the area.  The map above is the famous map made by Dr John Snow in 1854, during the cholera epidemic in London.
His research through mapping helped pinpoint the cause of the epidemic to a water pump located on Broad Street.

This map is located at:
http://scienceline.org/2010/05/john-snows-maps-of-the-broad-street-cholera-outbreak/