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 other data from the 1990 census. Effective June 30, 1993, these revised MA definitions for the Nation included 250 MSAs, 18 CMSAs (consisting of 73 PMSAs), and 12 NECMAs (plus 3 MSAs and 1 CMSA with 3 PMSAs in Puerto Rico).

The current MA standards, which will be in effect through the 2000 census, changed only slightly from those used for the previous decade. The most important changes were an expansion in the role of UAs in the qualification of outlying counties for inclusion in MAs, and certain alterations in the rules for titles. In addition, the current standards introduced the collective term MA.

The MA standards specify the step-by-step definition process by which the concept of a densely settled core area plus its suburbs becomes realized as individual MSAs, CMSAs, PMSAs, and NECMAs. Qualification of an MSA requires the presence of a city of 50,000 or more inhabitants, or a Census Bureau-defined UA (of at least 50,000 inhabitants) and a total population of at least 100,000 (75,000 in New England). The county or counties including the largest city in the core area of population become central counties of the MSA; so does any adjacent county that has at least 50 percent of its population in the UA surrounding the largest city. (In New England, the basic geographic unit for defining MSAs is the city or town rather than the county.)

Additional outlying counties are included in the MSA if they meet specified requirements of commuting to the central counties as well as other requirements of metropolitan character. The minimum level of commuting to central counties required to make a county eligible for consideration as an outlying county is 15 percent. In general, the lower the percentage of a county’s resident workers commuting to the central counties, the more demanding the other requirements of metropolitan character the county must meet in order to qualify for inclusion. The measures of metropolitan 13-6Metropolitan Areas