Social Explorer

The U.S. Census uses a system called "GEOGRAPHIES". They are boundaries that embody physical concepts, like zip codes known as ZTCA, cities, counties and states. However

• Social Explorer does not include every possible census geography
• The Census uses its own methods and terminology for geography as well, the most prominent of which is a division known as a "Census tract," which divides up counties
• Social Explorer shows boundaries for most Census Tracts back to 1940.
• City and Census Tract boundaries usually change with every decennial census.  Expect to see larger tracts for older census years.

• 010: Nation exp. United States of America
• 040: State - the primary legal subdivision of the United States
• 050: County - the primary legal subdivision of every state except Alaska and Louisiana.
• 070: Place -  An incorporated place is established to provide governmental functions for a concentration of people.
• 140: Census Tracts  are small, relatively permanent statistical subdivisions of a county 
  • Census tracts generally have a population size between 1,200 and 8,000 people, with an optimum size of 4,000 people. These are typically created by the census bureau.
• 310: Metropolitan Statistical Areas (MSA)
  • Metropolitan Statistical Areas contain core urban areas of 50,000 people or more. They consist of one or more counties in the core area as well as any adjacent counties which have a high degree of social and economic integration with the urban core (for example, the New York City metro contains parts of New Jersey as well).
• 850: Data by ZCTA (zip codes),
  • 5-Digit ZIP Code Tabulation Areas (ZCTA5) created by the Census Bureau are approximate area representations of U.S. Postal Service (USPS) ZIP Code service areas.