This article defines a "primary" metropolitan area as a metropolitan area that is not a component of a more extensive defined metropolitan area. A core-based statistical area (defined by the United States Office of Management and Budget (OMB)) that is not a component of a combined statistical area (CSA) is what is defined here as a "primary statistical area."
The 574 primary statistical areas (PSAs) of the United States and Puerto Rico comprise all 169 combined statistical areas currently defined by the OMB and the 405 of 929 core-based statistical areas (CBSAs) currently defined by the OMB that are not a component of a combined statistical area.
On February 28, 2013, the United States Office of Management and Budget defined 1098 statistical areas for the United States and Puerto Rico, comprising 169 combined statistical areas, 388 metropolitan statistical areas, and 541 micropolitan statistical areas for the United States and Puerto Rico. A total of 574 of these 1098 statistical areas qualify as primary statistical areas, including all 169 combined statistical areas, 122 of the 388 metropolitan statistical areas, and 283 of the 541 micropolitan statistical areas. The OMB does not use the term "primary statistical area", but the term is commonly used[who?] to identify the most extensive OMB-defined statistical area for a given county or county equivalent.