Study area
Philadelphia is the sixth largest city in the nation with a city population of 1.6 million inhabitants (U.S. Census Bureau, 2016) and hosts an average population density of 30,297 inhabitants per square kilometer. It is located at the confluence of the Delaware and Schuylkill rivers on the eastern border of Pennsylvania with the Appalachian Mountains to the west and the Atlantic Ocean to the east. The city has a total area of about 370 km2 of which 350 km2 are land and the rest, water.