Core-Based Statistical Areas (CBSA) partition counties into three categories: Metropolitan, Micropolitan, and Outside Core-Based Statistical Areas. Metropolitan and Micropolitan areas are composed of a core containing a population nucleus and adjacent communities that have a high degree of integration with the core. In this system, counties with cities or urbanized areas of over 50,000 residents are classified as Metropolitan, while counties with urban areas of 10,000 to 49,999 residents are classified as Micropolitan. Outlying counties are added to one of these urban classes when they are adjacent and when at least 25 percent of their resident labor force commutes to them. Although the remaining, Outside Core-Based Statistical Areas are often considered to be rural, this is not entirely correct, because these counties may include substantial population concentrations.
A county-based system such as CBSA, which attempts to describe the diversity in settlement patterns in a relatively large area by a single number, may not provide an informative depiction. A county may be designated as Metropolitan even though only a small portion is urbanized and the rest is distinctly rural. However, because county boundaries don't change much, every county will be represented by a measure, even after an extended period of time.
CBSA were developed by the Office of Management and Budget (OMB).
- Starting in the 2014 HCUP Databases, the CBSA designations are based on population and commuting information from the 2010 census and are defined according to the OMB 2013 Metropolitan definitions.
- In the HCUP databases prior to 2014, the CBSA designations are based on population and commuting information from the 2000 census and are defined according to the OMB 2003 Metropolitan definitions.