This interactive language map from the U.S. Census Bureau displays where, and to what degree, languages are spoken in a given area. "This is a web-based map application built to display language data from the American Community Survey. The maps contain dots that represent a specified number of people. The legend displays density value based on the level of zoom and scale. Dots are placed randomly inside of the tract they represent. Because tracts are small, you will see many dots clustered together in urban areas. The map is designed to show where there are concentrations of speakers in an area."
United States. Bureau of the Census: http://www.census.gov/
U.S. Census Bureau (2007-2011), American Community Survey