Dot Distribution Map

http://www.census.gov/geo/www/maps/2010_census_nighttime_map/nighttime_map_2010.html

A dot distribution map is a thematic map that displays quantitative data through the use of dots that represent a specific value. The maps show spatial patterns and are many times used to show populations of regions. In the 2010 U.S. Census map shown above, the population distribution across America is illustrated through the use of dots that represents a certain value or amount.  More populated areas have more dots, and therefore appear whiter than areas with a lower population distribution.