CBSA's are essentially fancy ways of referring to metro areas, but are used to refer to both those and newly-created micropolitan areas collectively. Micro areas are essentially defined as areas which have an urban area between 10,000 and 50,000 people. The total population of a micropolitan area can actually be larger than that, if the largest central city is small enough it will be referred to as micropolitan regardless.
The basic definition of metropolitan areas has had slight changes made to it as well. A metro area, as it did in 1990, requires an urban area of at least 50,000 people. Very large urban areas (2.5 million or more) are allowed to be split into "metropolitan divisions". These are akin to Consolidated Metropolitan Areas in 1990, but the standards are much less inclusive.
By a similar token, there are now definitions for "Combined Statistical Areas" (CSA). These areas can be formed when adjoining CBSA's meet particular standards to become new areas. It does not matter which kind of areas they are; any combination of metro and micro areas may be used to form a CSA.
Unlike past years, the traditional listings of metro areas list New England regions as county-based areas. In the past, these were referred to by the Census as "NECMA"'s (New England County Metropolitan Areas) and were separate from the normal census counts for the areas, which used cities and towns as their basis. They have essentially swapped places now, with the city and town areas (or NECTA's for New England City and Town Areas) being the separate listings.
Despite there not being much change in the basic definition, 49 new metropolitan areas were formed as a result of the new rules for them. Over 550 other areas were classified as micropolitan. All told, the present rules have defined 935 CBSA's in the U.S. and Puerto Rico. 11 of the CBSA's have metropolitan divisions, 29 in total. In comparison, the definition of metropolitan areas in 1999, the last year areas were formed based on the 1990 rules for them, there were 284 metropolitan areas, with 19 of the areas providing 76 primary metropolitan areas (the equivalent of divisions); almost three times the number of areas overall are now recognized by the OMB.