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 There are three types of codes for places. The first, the census place code, is a four-digit identifier that reflects the alphabetical order of all census places (including CDPs) within a State. The Census Bureau initially assigned these codes in increments of five to permit subsequent insertion of newly incorporated places or new CDPs. The Census Bureau revises these codes if it becomes necessary to maintain the alphabetic sequence for new places. The second, the governmental unit (GU) code, is used mainly in the Census of Governments and related surveys. This code is a three-digit identifier that is unique only within county; therefore, it must be used in conjunction with the remainder of the State, county, and MCD components of the code. The result is a nine-digit identifier. As the name implies, there are no GU codes for CDPs.

The USGS assigns the third type of code, the FIPS 55 code, which is a five-digit code assigned within a State considering the alphabetical sequence of names for all places, MCDs, and other named communities and locational entities such as well-known landmarks. There is a special set of class codes to distinguish between incorporated places, CDPs, MCDs, and the other classes of named entities. FIPS codes 90000–98999 are used for CCDs and some nonfunctioning MCDs; the USGS assigns the other numbers based on the alphabetic sequence of the locational entities within the individual States. FIPS codes are being adopted as a national standard for Federal agency data presentation, and will be used exclusively, in lieu of the census MCD and place codes, before the 2000 census.

The Census Bureau also assigns additional descriptive codes associated with places. Place size codes identify the population range (for example, a population of 500 to 999) within which each entity is located. Place description codes identify central cities of metropolitan areas and central places of UAs. In 1993, the Census Bureau produced the TIGER/GICS™ (Topologically Integrated Geographic Encoding and Referencing/Geographic Identification Code Scheme), a machine-readable file that contains the names of all places along with their census and FIPS 55 (but not GU) identification codes, and descriptive codes including those that identify place size, place description, and location within a metropolitan area. Each record also 9-32Places