Statistics for metropolitan areas (MAs) shown in the Statistical Abstract represent areas defined by the U.S. Office of Management and Budget (OMB) according to published standards that are applied to Census Bureau data. The general concept of an MA is that of a core area containing a large population nucleus, together with adjacent communities having a high degree of  economic and social integration with that core. Currently defined MAs are based on application of 1990 standards (which appeared in the Federal Register on March 30, 1990) to 1990 decennial census data and to subsequent Census Bureau population estimates and special census data. Current MA definitions were announced by OMB effective June 30, 1999. MAs include metropolitan statistical areas (MSAs), consolidated metropolitan statistical areas (CMSAs), and primary metropolitan statistical areas (PMSAs).

In this appendix, Table E presents geographic components and 1999 population estimates for each MSA, CMSA, and PMSA outside of New England. Table D presents definitions and data for New England county metropolitan areas (NECMAs), the county-based alternative metropolitan areas for the city- and town-based MSAs and CMSAs of the six New England states.

Standard definitions of metropolitan areas were first issued in 1949 by the then Bureauof the Budget (predecessor of OMB), under the designation ‘‘standard metropolitan area’’ (SMA). The term was changed to ‘‘standard metropolitan statistical area’’ (SMSA) in 1959 and to ‘‘metropolitan statistical area’’ (MSA) in 1983. The collective term ‘‘metropolitan area’’ (MA) became effective in 1990.

OMB has been responsible for the official metropolitan areas since they were first defined, except for the period 1977 to 1981, when they were the responsibility of the Office of Federal Statistical Policy and Standards, Department of Commerce. The standards for defining metropolitan areas were modified in 1958, 1971, 1975, 1980, and 1990.

Defining MSAs, CMSAs, and PMSA-The current standards provide that each newly qualifying MSA must include at least: one city with 50,000 or more inhabitants, or a Census Bureau-defined urbanized area (of at least 50,000 inhabitants) and a total metropolitan population of at least 100,000 (75,000 in New England). Under the standards, the county (or counties) that contains the largest city becomes the ‘‘central county’’ (counties), along with any adjacent counties that have at least 50 percent of their population in the urbanized area surrounding the largest city. Additional ‘‘outlying counties’’ are included in the MSA if they meet specified requirements of commuting to the central counties and other selected requirements of metropolitan character (such as population density and percent urban). In New England, the MSAs are defined in terms of cities and towns rather than counties. An area that meets these requirements for recognition as an MSA and also has a population of 1 million or more may be recognized as a CMSA if separate component areas can be identified within the entire area by meeting statistical criteria specified in the standards, and local opinion indicates there is support for the component areas. If recognized, the component areas are designated PMSAs, and the entire area becomes a CMSA. PMSAs, like the CMSAs that contain them, are composed of entire counties, except in New England where they are composed of cities and towns. If no PMSAs are recognized, the entire area is designated as an MSA. As of the June 30, 1999, OMB announcement, there were 258 MSAs, and 18 CMSAs comprising 73 PMSAs in the United States. In addition, there were three MSAs, one CMSA, and three PMSAs in Puerto Rico.

Central cities and MA titles-The largestcity in each MSA/CMSA is designated a ‘‘central city.’’ Additional cities qualify if specified requirements are met concerning population size and commuting patterns. The title of each MSA consists of the names of up to three of its central cities and the name of each state into which the MSA extends. However, a central city with less than 250,000 population and less than one-third the population of the area’s largest city is not included in an MSA title unless local opinion supports its inclusion. Titles of PMSAs also typically are based on central city names, but in certain cases consist of county names. Generally, titles of CMSAs are based on the titles of their component PMSAs.

Defining New England County Metropolitan Areas NECMAs-The OMB defines NECMAs as a county-based alternative to the city- and town-based New England MSAs and CMSAs. The NECMA for an MSA or CMSA includes: the county containing the first-named city in that MSA/CMSA title (this county may include the first-named cities of other MSAs/CMSAs as well), and each additional county having at least half its population in the MSAs/CMSAs whose first-named cities are in the previously identified county. NECMAs are not identified for individual PMSAs. There are 12 NECMAs, including 1 for the Boston-Worcester- Lawrence, MA-NH-ME-CT CMSA and 1 for the Connecticut portion of the New York- Northern New Jersey-Long Island, NY-NJCT- PA CMSA. Central cities of a NECMA are those cities in the NECMA that qualify as central cities of an MSA or a CMSA. NECMA titles derive from names of central cities.

Changes in MA definitions over time-Changes in the definitions of MAs since the 1950 census have consisted chiefly of the recognition of new areas as they reached the minimum required city or area population, and the addition of counties (or cities and towns in New England) to existing areas as new decennial census data showed them to qualify. In some instances, formerly separate MAs have been merged, components of an MA have been transferred from one MA to another, components have been dropped from an MA. The large majority of changes have taken place on the basis of decennial census data. However, Census Bureau population estimates and special censuses serve as the basis for intercensal updates.

Because of these historical changes in geographic definitions, users must be cautious in comparing MA data from different dates. For some purposes, comparisons of data for MAs as defined at given dates may be appropriate; for other purposes, it may be preferable to maintain consistent MA definitions.

In Tables A, B, and C below, data are given for MAs as defined for specific dates, thereby indicating the extent of change in population and land area resulting from revisions in definitions.