Definitions of Geographic Areas

Office of Management and Budget (OMB) Areas

Combined Statistical Areas - contains at least one Metropolitan Statistical Area and one or more of either Metropolitan or Micropolitan Statistical Areas.
Metropolitan Statistical Areas - a Metropolitan Statistical Area has at least one urbanized area of 50,000 persons or more, plus adjacent territory having a high degree of social and economic integration with the core as measured by commuting ties.
Micropolitan Statistical Area - This is a new Statistical Area category containing one or more urban clusters of at least 10,000 persons but less than 50,000 persons, plus adjacent counties having a high degree of social and economic integration with the core as measured by commuting ties.
Note: For the official definitions/descriptions of the current classification schema and how it came to be, see the Federal Register Report (pdf: 1.2 mb).
MSA_Definitions (pps: 180 kb) is a slide show that provides a short history of the MSA and explanation of the new categories.

Bureau of Economic Analysis (BEA) Areas

Economic Area (EA) - consists of one or more economic nodes (metropolitan areas or similar areas that serve as centers of economic activity) and the surrounding counties that are economically related to the nodes.

Component Economic Area (CEA) - consists of a single economic node (county) and the surrounding counties that are economically related to the node (county).