METROPOLITAN AREAS

The United States Office of Management and Budget (OMB) defines metropolitan
areas (MAs) 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, 1996. 

Standard definitions of metropolitan areas were first issued in 1949 by the
then Bureau of 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. MAs include metropolitan statistical areas (MSAs),
consolidated metropolitan statistical areas (CMSAs), and primary metropolitan
statistical areas (PMSAs). 

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 PMSAs 

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 one 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 one
or more counties, except in New England where they are composed of cities and
towns. If no PMSAs are recognized, the entire area is designated as a MSA. 

As of the June 30, 1996 OMB announcement, there were 255 MSAs, and 18 CMSAs
comprising 73 PMSAs in the United States. In addition, there were 3 MSAs, 1
CMSA, and 3 PMSAs in Puerto Rico. 


Central Cities and MA Titles 

The largest city 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 Area (NECMA) 

The OMB defines an NECMA as a county-based alternative for the city-based and
town-based New England MSAs and CMSAs. The NECMA defined 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 twelve
     NECMAs, including one for the Boston-Worcester-Lawrence, MA-NH-ME-CT
     CMSA and one for the Connecticut portion of the New York-Northern New
     Jersey-Long Island, NY-NJ-CT-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. 


Population Levels

MSAs, PMSAs, and NECMAs are categorized by their 1990 population, as follows:

     Level A - Areas of 1 million or more
     Level B - Areas of 250,000 to 999,999
     Level C - Areas of 100,000 to 249,999
     Level D - Areas of less than 100,000


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 urbanized 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, or 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. 

Source: U.S. Census Bureau 
