Study area
Philadelphia PA, USA is the sixth largest city in the United States 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. Phildelphia is one of the poorest cities in the US, with 26 percent of its population living in poverty (PEW, 2017). Philadelphia is also one of the most segregated cities in the US, with African American and Asian populations concentrated in neighborhoods in West and North Philadelphia respectively (The Brookings Institution, 2003). The city’s population peaked in 1950 with over 2 million people, and was declining until 2010 when is started growing again. Recently, Philadelphia is experiencing strong, yet uneven economic resurgence reflected in job growth and rising housing prices (PEW, 2017).
Philadelphia’s urban structure emerged through the evolution of its original plan, laid out by William Penn in 1643. It has a gridded layout with mostly low and mid-rise residential buildings. A long time “gentleman’s agreement” kept Penn’s statue on top of city hall as the highest building in the city, preventing high-rise development for decades until the 1980s. The most common residential structures in the city are rowhouses. Rowhouses commonly occupy a narrow street frontage and are attached to other homes on both sides (Simmons Schade et al., 2008). Aside from the build environment, green space in the city includes 19% tree cover and 24% grass-shrub cover that are distributed unevenly across the city with some neighborhoods densely vegetated and others with little to no green space (O’Neil-Dunne, 2011). Part of the city’s sustainability plan, Greenworks Philadelphia, includes a goal of tree canopy cover of 30% in all city neighborhoods by 2025 (City of Philadelphia, 2015a). However, until recently, the only publicly available data for a comprehensive analysis of the city’s green space has been the National Landuse-Landcover (NLCD) datasets that do not have the spatial resolution and functional categories required to identify small and fragmented patches of landscape elements within the city. In 2011, a fine scale dataset of Philadelphia landcover was released (City of Philadelphia, 2011) that is used here as the basis for the STURLA classification system. Empirical evidence from two cities, Berlin and New York City (NYC), were compared (Larondelle et al., 2014) and more detailed analysis of within class and neighborhood effects were performed in a Berlin case study (Kremer et al., 2018).