|Pennsylvania is the sixth most populous state in the United States with an estimated population of over 12.4 million residents. The state also ranks high in population density with a position of 10 among the most densely populated states of the US. Located in the Northeastern and Middle Atlantic regions of the country, it is bounded by Ohio on the west, West Virginia on the southwest, New York and Canada to the north, Delaware and Maryland to the south and New Jersey on the east. It also has a coastline along Lake Erie and a shoreline along the Delaware Estuary. The Commonwealth of Pennsylvania was among the thirteen states that laid the foundation of the United States of America and was only second to enter the Union in 1787. The highest point in the state is Mount Davis, which is at a height of 3,213 feet above sea level. The lowest point is on the Delaware river. Commonly known by the abbreviation PA or Penna and by the nickname "Quaker State", Pennsylvania has been a Keystone State since 1802. Philadelphia is the most populated city and Harrisburg is the capital of the state.