§                  United States - The United States comprises the 50 states and the District of Columbia. §                  States - The primary divisions of the United States. The District of Columbia is treated as a state. §                  Counties - The primary political administrative subdivision of a state, the county is widely used for marketing purposes for the following reasons: §                           The range and reliability of currently available data below the state level is greatest at the county level. §                           County geographic boundaries are rarely altered. §                           Complete national coverage is achieved by summarizing all counties. §                           County boundaries are readily identifiable. NOTE: For Louisiana, parishes are used in lieu of counties; for Alaska, boroughs and census areas. The District of Columbia is treated as a single county unit. In Virginia, all cities are by law independent of counties; therefore they are treated as county units. The cities of Baltimore, MD, St. Louis, MO and Carson City, NV are also independent and therefore classified as counties. §                  Places - The Bureau of the Census defines a place as a concentration of population; a place may or may not have legally prescribed limits, powers, or functions.  This concentration of population must have a name, be locally recognized, and not be part of any other place. §                  CBSAs (Core-Based Statistical Areas) - The Office of Management and Budget (OMB) reviewed the Metropolitan Area standards in 1999 and 2000. The new standards replace the current metropolitan area classification with a Core-Based Statistical Area (CBSA) classification. SRC has included both the existing MSA definitions as well as the new CBSA definitions. The new Core-Based Statistical Area (CBSA) consists of a county containing an Incorporated Place or Census Designated Place with a population of at least 10,000 along any adjacent counties that have at lease 25% of employed residents of the county who work in the CBSAs core or central county. CBSAs are categorized as being either Metropolitan (core population of at least 50,000) or Micropolitan (core population between 10,000 and 50,000). this allows common statistics to be collected for less urban areas of the nation. These two county-based CBSA definitions will cover approximately 90% of the U.S. population. §                  Census Tracts - A small, permanent subdivision of a county with homogeneous population characteristics, status and living conditions. §                  Block Groups - Subdivisions of Census Tracts, each generally contain between 600 and 3000 people, with an optimum size of 1,500 people. §                  DMAs - Designated Market Areas, the formal term for what is more commonly known as a TV or broadcast market. Definitions for DMA's are supplied by Nielsen Media Research that generates ratings for broadcast programming. DMA's are selected by totaling the viewer hours of TV stations whose signals reach a particular county with total hours, then converted to a percentage share of all viewing hours. DMA's are named for the market of origin of the station(s) with the largest share of viewer hours, and all counties whose largest viewer share is given to stations in that same market of origin are grouped together under that DMA. NOTE: Because of the reach of broadcast signals, DMA's don't always conform to whole-county geography like metro markets or newspaper markets. In certain cases, Nielsen splits counties, treating each portion as if it were a separate county. Each county, or portion thereof, is allocated to a single DMA, eliminating any geographic overlap. DMA's cover the whole U.S., except for parts of Alaska. §                  MSAs - Metropolitan Statistical Areas are geographic areas each with a significant population nucleus, along with any adjacent communities that have a high degree of economic and social integration with that nucleus. §                  ZIP Codes - Administrative units established by the United States Postal Service (USPS) for the efficient distribution of mail. ZIP Codes generally do not respect political or census statistical area boundaries, nor do they usually have clearly identifiable boundaries. In addition, ZIP Codes often serve a continually changing area, are changed periodically to meet postal requirements and do not cover all the land area of the United States. The first three digits of the five-digit code identify a major city or sectional distribution center while the last two digits signify a specific post office delivery area or point. §                  Custom Radius - A specific street address or intersection with data aggregated for 1 or multiple radii from it or bands around it.  For a more detailed explanation of these geographies please visit the U.S. Census Bureau's Geographic Areas Reference Manual.