freestanding metropolitan statistical areas (MSAs) or as consolidated metropolitan statistical areas (CMSAs) and their constituent primary metropolitan statistical areas (PMSAs). In the six New England States, the geographic building blocks of MAs are MCDs or statistically equivalent entities, rather than counties as in other States. This practice harmonizes with the situation existing in New England, where the MCDs are the primary units of local government (for details, see Chapter 13, “Metropolitan Areas”).
The picture varies with regard to the geographic entities that the Census Bureau uses in its urban and rural classifications. There is no necessary geographic relationship between county subdivisions and urbanized areas (UAs) because the geographic components of UAs are places and census blocks. The same is true of non-UA urban places, which are entities that have 2,500 or more residents, because places often are subdivided by MCD/CCD boundaries.
The boundaries of other types of geographic entities sometimes conform to county subdivision boundaries. For example, MCD boundaries also may be used to bound Congressional districts. Smaller entities—voting districts, school districts, and ZIP Codes—may sometimes constitute an MCD or portions of their boundaries may coincide with MCD or CCD boundaries.
