Pittsburgh is the second-largest city in the US Commonwealth of Pennsylvania and
the county seat of Allegheny County. Regionally, it anchors the largest urban area
of Appalachia and the Ohio River Valley, and nationally, it is the 22nd-largest
urban area in the United States. The population of the city in 2010 was 305,704,
while that of the seven-county metropolitan area stood at 2,356,285. Downtown Pittsburgh
retains substantial economic influence, ranking at 25th in the nation for jobs within
the urban core and 6th in job density.
The characteristic shape of Pittsburgh’s central business district is a triangular
tract carved by the confluence of the Allegheny and Monongahela rivers, which form
the Ohio River. The city features 151 high-rise buildings, 446 bridges,two inclined
railways, and a pre-revolutionary fortification. Pittsburgh is known colloquially
as “The City of Bridges” and “The Steel City” for its many
bridges and former steel manufacturing base.