Dot Distribution map

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

Dot Distribution maps are used to show a location of a certain data over a geographic area. Dot distribution maps likely are a single dot located on a map that show a specific data point. The map above was used to show where feeder watchers were located across North America. Each dot represents the zip code of someone who signed up to participate in the feeder watcher program. So each single dot represents one persons home, but as the dots become more condensed it becomes clumped.