Pittsburgh is the second-largest city in the U.S. Commonwealth of Pennsylvania, after Philadelphia, and the county seat of Allegheny County. Regionally, it anchors the largest urban area of both Appalachia and the Ohio River Valley. Nationally, it is the 27th-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.
While the city is historically known for its steel industry, today its economy is largely based on healthcare, education, technology, robotics, and financial services. The downturn of the steel industry left no steel mills within city limits and only two remaining mills (the Edgar Thomson Steel Works and Brackenridge Works) in the county, though more than 300 steel-related businesses remain in the area. By contrast, the region now supports 1,600 technology and research companies, ranging from major campuses for Google, Intel, RAND, Apple and Disney Research to small startups. In the last few decades the city has redeveloped abandoned industrial sites with new housing, shopping, and offices, such as SouthSide Works, Bakery Square and the Pittsburgh Technology Center.
While Pittsburgh faced an economic crisis in the 1980s as regional industries waned, modern Pittsburgh is economically strong. The housing market is relatively stable as of 2012, despite a national subprime mortgage crisis, and Pittsburgh added jobs in 2008 even as the national economy entered a significant jobs recession. This positive economic trend is a recovery from the 1974-1998 period, when Pittsburgh lost its manufacturing base in steel and electronics, and its status as the third-largest center for corporate jobs after New York and Chicago with corporate raiders removing the global headquarters of J&L Steel (1974), Gulf Oil (1984), Murphy's Mart (1985), Koppers Chemical and Rockwell Aerospace (both 1988), Sunbeam (1991), Westinghouse (1995) and Dravo Shipbuilding (1998), all through multi-million dollar deals.
The city's strength today is built on headquarters to major global financial institutions PNC Financial Services (the nation's fifth-largest bank), Federated Investors, Highmark Insurance and the regional headquarters of BNY Mellon, descended from Mellon Financial and the Mellon family, as well as headquarters to six major law firms all ranking in the top 300 of the nation, including K&L Gates and Reed Smith. A strong charitable foundations base along with long running arts and cultural amenities are complemented by seven venerable universities in the city, all providing graduate level and post graduate level resources and an additional 15 in the metro area. The world renowned Carnegie Library and the Carnegie Museums provide deep cultural, economic and academic strengths to the city.
Major publications often note Pittsburgh's high livability compared to other American cities, with the city claiming the top overall spot in the United States in recent "most livable city" lists by Places Rated Almanac (2007), Forbes (2010), and The Economist (2011). In 2012, National Geographic named Pittsburgh one of the best worldwide travel destinations.