The Commonwealth of Pennsylvania, often colloquially referred to as PA (its postal abbreviation which succeeds the archaic Penn. and Penna. as common abbreviations) by natives and Northeasterners, is a state located in the Northeastern and Middle Atlantic regions of the United States.
Pennsylvania has been known as the Keystone State since 1802, based in part upon its central location among the original Thirteen Colonies forming the United States. Pennsylvania is also nicknamed the "Keystone State" because of the number of important American documents signed in the state (such as the Declaration of Independence). It was also a keystone state economically, having both the industry common to the North, making such wares as Conestoga wagons and rifles, and the agriculture common to the South, producing feed, fiber, food, and tobacco.
Another one of Pennsylvania's nicknames is the Quaker State; in colonial times, it was known officially as the Quaker Province, in recognition of Quaker William Penn's First Frame of Government constitution for Pennsylvania that guaranteed liberty of conscience. He knew of the hostility Quakers faced when they opposed religious ritual, taking oaths, violence, war and military service, and what they viewed as ostentatious frippery.
Philadelphia in the southeast corner, Pittsburgh in the southwest corner, Erie in the northwest corner, Scranton-Wilkes-Barre in the northeast corner, and Allentown-Bethlehem-Easton in the east central region are urban manufacturing centers. Much of the Commonwealth is rural; this dichotomy affects state politics as well as the state economy. Philadelphia is home to eight Fortune 500 companies, with more located in suburbs like King of Prussia; it's a leader in the financial and insurance industry. Pittsburgh is home to seven Fortune 500 companies, including U.S. Steel, PPG Industries, H.J. Heinz, and Alcoa. In all, Pennsylvania is home to fifty Fortune 500 companies.
As in the US as a whole and in most states, the largest private employer in the Commonwealth is Wal-Mart, followed by the University of Pennsylvania, United Parcel Service and Giant Food (called Stop and Shop in other states). The largest manufacturing employer is Merck.
Pennsylvania is home to the nation's first zoo, the Philadelphia Zoo. Other long-accredited AZA zoos include the Erie Zoo and the Pittsburgh Zoo & PPG Aquarium. The Lehigh Valley Zoo and ZOOAMERICA are other notable zoos. The Commonwealth boasts some of the finest museums in the country, including the Carnegie Museums in Pittsburgh, the Philadelphia Museum of Art and several others. One of the unique museums is the Houdini Museum in Scranton, the only building in the world devoted to the legendary magician. Pennsylvania is also home to the National Aviary, located in Pittsburgh.
Municipalities in Pennsylvania are incorporated as cities of several classes, boroughs, as townships of several classes, or under home rule charters. A "Village", often identified by a roadside sign, is unincorporated, and is merely a locale without distinct boundaries. There are 2,567 municipalities in the state.
There is some confusion about the number of "towns" in Pennsylvania. In 1870, Bloomsburg, the county seat of Columbia County was incorporated as a town, and is recognized by state government publications as "the only incorporated town" in Pennsylvania. However, in 1975, McCandless Township, in Allegheny County adopted a home rule charter under the name "Town of McCandless".
The ten most populated cities in Pennsylvania, in order are: Philadelphia, Pittsburgh, Allentown, Erie, Reading, Scranton, Bethlehem, Lancaster, Altoona, and Harrisburg.