In the United States, a metropolitan statistical area (MSA) is a geographical region with a relatively high population density at its core and close economic ties throughout the region. Such regions are not legally incorporated as a city or town would be and are not legal administrative divisions like counties or separate entities such as states. As a result, sometimes the precise definition of a given metropolitan area will vary between sources. The statistical criteria for a standard metropolitan area were defined in 1949 and redefined as a metropolitan statistical area in 1983.