The Pittsburgh metropolitan area (also called Greater Pittsburgh, Southwestern Pennsylvania or the Pittsburgh Tri-State) is the largest population center in both the Ohio River Valley and Appalachia. The metropolitan area consists of the city of Pittsburgh in the Commonwealth of Pennsylvania and surrounding counties. By many definitions the area extends into the U.S. states of West Virginia and Ohio. The larger "tri-state" region is defined by the U.S. Census as the Combined Statistical Area (CSA) while definitions of the Metropolitan Statistical Area (MSA) are within Pennsylvania.