Beginning in 1950, the United States Census Bureau has delineated standard metropolitan areas using comparable principles.

• In the 44 states outside New England, standard metropolitan areas are based upon county borders.

• In the six New England states, standard metropolitan areas are based upon municipal borders (Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont).

  The use of muncipal boundaries results in a closer correlation between the municipality based urbanized area than the county definitions used outside New England or the NECMAs.

Demographia uses the terms "metropolitan area" or "census metropolitan area" to denote standard metropolitan areas and "county metropolitan areas" to denote county based metropolitan areas (standard metropolitan areas in 44 states and county metropolitan areas in the six New England states).

Types of Standard Metropolitan Areas

MSA: Metropolitan Statistical Area: A non-consolidated metropolitan area, such as St. Louis or Atlanta. Based upon county boundaries in 44 states and municipal boundaries in New England.

CMSA: Consolidated Metropolitan Statistical Area: A consolidated metropolitan area, which includes more than one PMSA, such as New York or Los Angeles. Based upon county boundaries in 44 states and municipal boundaries in New England.

PMSA: Primary Metropolitan Statistical Area: A component part of a consolidated metropolitan area, such as San Jose (in the San Francisco CMSA) or Kenosha in the Chicago CMSA. Based upon county boundaries in 44 states and municipal boundaries in New England.

NECMA: New England County Metropolitan Area: A metropolitan area in New England (Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont) based upon county boundaries.

Density of Metropolitan Areas

There is little value in calculating densities of standard metropolitan areas, at least outside New England. This is because they are based upon county boundaries. To include all of the urban population in a metropolitan area, it is necessary to include non-urban parts of some counties, with the effect that large portions of metropolitan areas are rural land. For example, the Los Angeles CMSA has a population of approximately 16 million (1999), with a land area of approximately 34,000 miles, for a population density of less than 500 persons per square mile (component San Bernardino and Riverside counties extend across nearly 200 miles of largely uninhabited desert to the Nevada and Arizona borders). This is an area almost as large as the state of Indiana. As a result, the Los Angeles CMSA is among the least dense metropolitan areas. However, the urbanized area of Los Angeles (developed area) is the most dense in the nation.