Dot distribution maps

http://www.census.gov/geo/www/mapGallery/2kpopden.html

Dot distribution maps display some type of numerical information—such as population or areas of important resources—by placing dots in areas that the subject was recorded. These dots also have a numerical value associated with them and a unit type, both of which are usually found on the map itself. This map shown is a dot distribution map for the 2000 Census of the US Population. One dot represents 7,500 people nearby to the dot, so it is easy to see where people were most dense in the United States in the year 2000.