The Commonwealth of Pennsylvania ( /ˌpɛnsɨlˈveɪnjə/ (help·info)), 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. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and a water border with Canada to the north, and New Jersey to the east. The state's most populous city is Philadelphia, followed by Pittsburgh.
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, and also in part 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).
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