Pittsburgh is the second largest city in the U.S. state of Pennsylvania with a population of 312,819. The population of the eight-county metropolitan area is 2,462,571.The city's Downtown retains substantial economic influence, ranking at 25th in the nation for jobs within the urban core (and is sixth in job density).---------- The characteristic shape of downtown is a triangular tract carved by the confluence of the Allegheny and Monongahela Rivers, where the Ohio River forms. The skyline 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 it is largely based on healthcare, education, technology, robotics, fashion, and financial services. The city has made great strides in redeveloping abandoned industrial sites with new housing, shopping and offices, such as the SouthSide Works. While Pittsburgh faced economic troubles in the mid 1970s as the steel industry waned, modern Pittsburgh is economically strong. The housing market is relatively stable despite a national sub-prime mortgage crisis, and Pittsburgh has added jobs in 2008 even as the national economy is in a significant jobs recession.This positive economic news is in contrast to 30 years ago when Pittsburgh lost its manufacturing base as those jobs moved offshore. ------------ In 2007, Forbes magazine named Pittsburgh the 10th cleanest city, and in 2008 Forbes listed Pittsburgh as the 13th best city for young professionals to live. The city is consistently ranked high in livability surveys. In 2007, Pittsburgh was named "America's Most Liveable City" by Places Rated Almanac.