The United States Office of Management and Budget (OMB) defines micropolitan and metropolitan statistical areas. Metropolitan and micropolitan statistical areas consist of one or more counties. Currently defined metropolitan and micropolitan statistical areas are based on application of the 2000 standards (which appeared in the Federal Register on December 27 2000) to Census 2000 data, as updated by application of those standards to more recent Census Bureau population estimates. The current definition is as of December 2005.

If specified criteria are met, adjacent metropolitan and micropolitan statistical areas, in various combinations, may become the components of a new set of areas called combined statistical areas (CSAs). Using Census Bureau data the OMB compiles lists of CSAs. The areas that combine retain their own designations as metropolitan or micropolitan statistical areas within the larger combined statistical area. There are 125 CSAs defined by OMB as of December 2005.

Note that CSAs represent multiple metropolitan areas that have a high degree of employment interchange. CSAs often represent regions with common labor and media markets. The use of CSAs as a representation for a single metropolitan area is not always appropriate.

Largest CSAs

The following is a list of the 25 most populous combined statistical areas in the United States, according to the July 1, 2004 U.S. Census Bureau estimates:

The list of most populous CSAs is similar to, and may easily be confused with, a list of the most populous conurbations of the US, but is in fact not identical, because it excludes MSAs that are not part of a larger CSA. The following MSAs are larger than some of the above CSAs:

External links

• List of Combined Statistical Areas
• US Office of Management and Budget
• US Census Bureau

Demographics of the United States | Metropolitan areas of the United States