Census tracts are uniquely numbered within a county and are typically a 4-digit number ranging in value from 1 to 9999. Some Census Tracts have a 2-digit suffix. A decimal point is used to delineate between the basic 4-digit number and the 2-digit suffix. From the 2000 Census, there are 66,304 Census Tracts.

Census Place - an incorporated place with an active government and definite geographic boundaries such as a city, town, or village. Census Places may be subdivisions of MCD's, or in some situations they are the same as MCD's. In addition, the Census Bureau recognizes unincorporated places that have no definite boundaries or government. These are known as Census Designated Places (CDP). There may be a relationship between Census Place boundaries and Census Tract boundaries, but Census Tract and Census Place boundaries do not necessarily correspond. There are roughly 25,000 Census Places in the U.S.

Congressional Districts - a geographic area represented by an elected member of the U.S. House of Representatives. There are 435 Congressional Districts in the U.S., which are apportioned to each State based on their 2000 Census population. The states create Congressional Districts by aggregating Census Blocks or Voting Districts. A Congressional District on average contains approximately 650,000 people. The 108th Congress, which took office in January of 2003, is the first to represent Congressional Districts created using data from the 2000 Census.

Congressional Districts can cross city, town, township, and county boundaries, but do not cross State boundaries. Congressional Districts in rural parts of states may be made up of whole Counties while those in urban and suburban areas tend to split counties, cities, etc.

Designated Market Area (DMA) – a geographic area that represents individual television markets as defined by Nielsen Media Research. DMA’s are typically defined by county and the market definitions are updated each fall by NMR. Due to topography, television signals may not reach all parts of a county resulting in some counties being split and assigned to multiple DMA's. There are 210 DMA markets in the U.S.

FIPS State/County Code – a unique 5 digit code comprised of a 2 digit state code and a 3 digit county code that is assigned to every county (and county equivalent) in the U.S. Federal Information Processing System (FIPS) codes are assigned and managed by the Federal Government. There are 3,144 counties (and county equivalents) in the U.S.

Metropolitan Areas - The basic concept of metropolitan is one of a population nucleus and the surrounding territory that has an economic and social relationship with the nucleus. The Office of Management and Budget (OMB) defines Metropolitan Areas.

In June of 2003, the OMB adopted new standards for Metropolitan Areas and established Core Based Statistical Areas (CBSA). These standards replace and supercede the previous standards used to define Metropolitan Statistical Areas (MSA).

CBSAs are divided into two categories – Metropolitan Statistical Areas and Micropolitan Statistical Areas. All CBSAs are comprised of one or more counties, except in the six (6) New England states where the OMB has developed a similar set of metropolitan areas known as New England City and Town Areas (NECTAs), comprised of cities and towns.

CBSAs incorporate a new 5-digit coding scheme that is unique across both Micropolitan and Metropolitan Statistical Areas. For the most part, the geographic definitions and names of the new Metropolitan Statistical Areas mirror the "old" MSA geographies. However, it should be noted that in some cases there is a significant difference in the geographic composition of the new Metropolitan Statistical Areas. Micropolitan Statistical Areas are new and contain counties that were previously non-metropolitan.

Metropolitan Statistical Area (MSA) – A Core Based Statistical Area (CBSA) associated with at least one urbanized area with a population of at least 50,000, based on the 2000 Census. A Metropolitan Statistical Area is comprised of the Central County or counties containing the core urban area, plus adjacent/outlying counties that have a high degree of social and economic integration with the Central County, as measured by commutation patterns. As of June 6, 2003, the OMB has defined a total of 362 Metropolitan Statistical Areas that incorporate 1,090 counties, containing approximately 83% of the US population. While 78% of the counties now classified as "metropolitan" are the same as before, many Metropolitan areas have changed in some way, either by name or geographic composition.

Micropolitan Statistical Area (MCSA) – A Core Based Statistical Area with at least one urban cluster containing between 10,000 to 50,000 people, based on the 2000 Census. A Micropolitan Statistical Area is comprised of the Central County or counties containing the core urban area, plus any adjacent/outlying counties with a high degree of social and economic integration as determined again by commutation patterns. As of June 6, 2003, there are 560 Micropolitan Statistical Areas (all new) comprising 674 counties and containing 10% of the US population.

Some of the larger Metropolitan Statistical Areas are subdivided into Metropolitan Divisions that mirror "old" MSA geography. These Metropolitan Statistical Areas are similar in geographic composition to the "old" Consolidated Metropolitan Statistical Areas (CMSAs). For example, the Dallas-Fort Worth-Arlington MSA is comprised of the Dallas-Plano-Irving and Fort Worth-Arlington Metropolitan Divisions. The county definitions for these divisions are identical to the "old" Dallas and Fort Worth MSAs.

Metro Status Code - a one-digit code developed by MSG that sub-classifies an MSA or MCSA. The description is as follows:

Minor Civil Division (MCD) - Minor Civil Divisions exist only in 28 states of the U.S. MCD's have legal boundaries and are known under various terms including Towns, Townships, Boroughs, Cities, etc. Census Tract boundaries generally correspond to MCD boundaries, but Census Tract boundaries may cross and can include more than one MCD. In states without MCD's the Census Bureau has created Census County Divisions (CCD). A CCD is an area created using combinations of Census Tracts, has no legal boundaries, and functions primarily for the collection and tabulation of Census statistics. There are roughly 31,000 MCD's and 5,500 CCD's in the U.S.

Nielsen County Size - a one character code developed and assigned to each county by Nielsen Media Research.

ZIP Codes - an acronym for Zone Improvement Plan. The U.S. Postal Service introduced ZIP Codes in the early 1960's as a means of improving mail delivery. ZIP Code boundaries change often and can cross City, Town, Township, and County boundaries and in rare situations cross State boundaries. There is no correlation between Census geography and Postal Geography. There are roughly 42,000 ZIP codes in the U.S. However, approximately 10,000 of these are non-delivery ZIP Codes (i.e. P.O. Boxes) or businesses and office buildings with high volumes of mail. Non-delivery ZIP Codes do not have any households or population associated with them.

ZIP Codes are 5 digit numbers and occur in a range from 01001 to 99999. The first digit indicates one of ten geographic regions of the U.S. The next two digits indicate smaller geographic regions within a State. The first three numbers combined are known as the Sectional Center Facility (SCF), which is a facility where mail is sorted before it is sent on to local Post Offices. The fourth and fifth digits of the ZIP Code identify the local Post Office.

ZIP+4 - a 4 digit suffix added to ZIP Codes that allow for more detailed sorting of mail. The first two digits of the +4 code are a Section, which may be a group of streets, several city blocks, a housing development, an apartment complex, or an office building, etc. The last two digits are the delivery Segment which indicate a hundred block range, a side of a street, a floor of an office building, a building in an apartment complex, a post office box, etc. There are over 65 million ZIP+4 codes in the U.S.