Melissa Data Updates Geocoding Products to Reveal 2010 Census Data
Data is only as accurate as the geography is rests on, so currency in geography matters as much as accuracy in data. Geographic boundaries and inventory have changed drastically in the 10 years between each decennial census, particularly at smaller geography levels, such as census tracts, block groups, and blocks.
Even if boundaries do not change, the Census Bureau can renumber geographic codes for areas. It is essential users be cognizant of geographic differences between 2000 and 2010 when analyzing trends.
Census 2010 data revealed dramatic new demographic trends for the United States. Changes such as increased population diversity; post-Katrina migrations, and effects of the recession, including reduced household incomes and the housing market crash, occurred in the United States between 2000 and 2010. Data from Census 2010 captured these changes for the entire country. Why are these changes so important? If an analyst uses data from Census 2000, events such as the growth of the Hispanic population, increased home vacancy rates, and lower household income would be overlooked.
Political areas like cities or townships change whenever local governments elect to revise their boundaries. Larger political areas like counties change less often than places, but boundary revisions are not uncommon. ZIP Codes, which are defined solely to expedite mail delivery, can change monthly or whenever the U.S. Postal Service sees fit to revise delivery routes. Metropolitan areas are usually revised annually, although the Office of Management and Budget overhauls the definitions decennially, with data from the census.
Census 2010 Geographies and Changes
A census block is a component of a block group, identified by a four-digit code. Blocks are small in area, in general, especially in cities. However, blocks in rural or remote areas may cover hundreds of square miles. A block code that starts with a zero indicates a water-only block. There are 11,078,297 blocks in Census 2010 geography, as opposed to 8.2 million in Census 2000.
Block Groups (BGs)
A block group is a collection of one or more blocks and a statistical division of a census tract, identified by a one-digit code. Block groups do not cross census tract, county, or state boundaries. In general, a block group is comprised of 600 to 3,000 residents. A zero block group code indicates a water-only BG. Boundary changes and code restructuring are reflected in the Census 2010 release. There are 217,740 block groups in Census 2010 geography.
Census tracts are small statistical subdivisions of a county, with 1,200 to 8,000 residents typically. The boundaries are usually delineated by local committees, and do not cross county or state lines. Tracts are identified by a six-digit code, with an implied decimal between the fourth and fifth digit. Boundary changes and code restructuring are reflected in the Census 2010 release. There are 73,057 tracts in Census 2010 geography.
Counties are the primary legal divisions of a state, identified by a two-digit state FIPS code and a three-digit county FIPS code. Boundary changes, as well as code and name changes, occurred in Alaska. Specifically, 3 codes were dropped and 5 new codes and names were added. There was also a slight change to a county name in Illinois and New Mexico. There are 3,143 counties in Census 2010 geography.
County Subdivisions (CSDs)
County subdivisions are the primary divisions of counties, and include census county divisions (CCDs), minor civil divisions (MCDs), census subareas, and unorganized territories. CCDs exist in 20 states, MCDs are in 29 states, census subareas exist only in Alaska, and unorganized territories are in 9 states. CSDs can be uniquely identified using a two-digit state FIPS code, three-digit county FIPS code, and five-digit CSD FIPS code. Boundary changes, as well as code and name changes, are reflected in the Census 2010 release. There are 35,703 county subdivisions in Census 2010 geography.
Places (Cities and Towns)
Places include incorporated places (usually cities, towns, villages or boroughs), census designated places, and balance portions of consolidated cities. Places are uniquely identified using a two-digit state FIPS code and five-digit place FIPS code. Boundary changes, as well as code and name changes, are reflected in the Census 2010 release. There are 29,261 places in Census 2010 geography, compared to 25,150 in Census 2000.
Core Based Statistical Areas (CBSAs)
Core Based Statistical Areas, which include metropolitan and micropolitan statistical areas, are comprised of one or more counties and are defined by the U.S. Office of Management and Budget (OMB). A metropolitan statistical area is affiliated with at least one urbanized area of 50,000 or more inhabitants. A micropolitan statistical area is associated with at least one urban cluster of at least 10,000 people, but less than 50,000. There were no boundary, code or name changes made to CBSAs since the last release. The total number of CBSAs stands at 942, each identified by a five-digit code.
Designated Market Areas (DMAs)
Designated Market Areas are television markets defined by The Nielsen Company, revised on an annual basis. The current vintage is the 2010-2011 DMA definitions. The majority of DMAs are comprised of one or more whole counties, although a few include parts of counties. Boundary changes, but no name or code changes, are reflected in this release. There are 210 DMAs, each identified by a three-digit code.
Congressional Districts (CDs)
Congressional districts are the areas from which individuals are elected to the U.S. House of Representatives, currently the 112th Congress. Once the apportionment of congressional seats is made based on census population counts within a state, then each state will establish CDs to elect representatives. A congressional district is uniquely identified using a two-digit state FIPS code and two-digit CD FIPS code. There are 436 CDs in this release.
Residential ZIP Codes
Created by the U.S. Postal Service to deliver the mail, ZIP Codes do not represent standard census geographic areas for data reporting. Because ZIP Code boundaries are not contiguous with census geographic areas or stable over time, data estimated for ZIP Codes are also subject to change. Residential ZIP Code data are estimated from block group data, using a correspondence file created by assigning Census 2010 block points to ZIP Code boundaries from Navteq. The vintage of the ZIP Code boundaries is December 2010. The total number of residential ZIP Codes in this release is 31,890.