Dot Distribution Maps

Dot distribution maps are also known as dot density maps. These maps use dots to indicate the geographical occurances  or presence of some phenomenon or characteristic. They are thematic maps which use dots to diplay data.

 

http://www.birds.cornell.edu/pfw_fr/Members/ParticipantMap00.htm 

This dot distribution maps uses red dots by zip code to show where people who participate in a bird watching program live. It seems the geographical density of watchers is highest in the NE, like many other phenomena.