Pittsburgh, Pennsylvania, the second largest city in the state and the seat of Allegheny County. It is in the southwestern part of the state, where the Monongahela and Allegheny rivers merge to form the Ohio River.

Pittsburgh is built mainly on rolling to hilly land. Level land is mostly in the river valleys and in the wedge—called the Golden Triangle—where the rivers meet. The city's original site is in the Golden Triangle, which is now occupied by the business district. Industrial areas have developed mainly along the three rivers; residential areas are spread throughout the hills. Among the many suburbs and cities in the Pittsburgh area are Baldwin, Bethel Park, McKeesport, Monroeville, Mount Lebanon, Penn Hills, and West Mifflin.