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 area. Such regions are neither legally incorporated as a city or town would be, nor are they legal administrative divisions like counties and states. As such, the precise definition of any given metropolitan area can vary with the source. A typical metropolitan area is centered on a single large city that wields substantial influence over the region (e.g., Chicago or Atlanta). However, some metropolitan areas contain more than one large city with no single municipality holding a substantially dominant position (e.g., Dallas–Fort Worth metroplex, Riverside–San Bernardino or Minneapolis–Saint Paul). MSAs are defined by the Office of Management and Budget (OMB) and used by the Census Bureau and other federal government agencies for statistical purposes.