The United States Office of Management and Budget (OMB) has defined 917 Core Based Statistical Areas (CBSAs) for the United States and 12 for Puerto Rico. The OMB defines a Core Based Statistical Area as one or more adjacent counties or county equivalents that have at least one urban core area of at least 10,000 population, plus adjacent territory that has a high degree of social and economic integration with the core as measured by commuting ties. The 929 Core Based Statistical Areas currently defined by the OMB include the 388 Metropolitan Statistical Areas (MSAs), which have an urban core population of at least 50,000, and the 541 Micropolitan Statistical Areas (μSAs), which have an urban core population of at least 10,000 but less than 50,000.