"These files contain 2004 digital orthoimagery of the City of Philadelphia and surrounding watershed area. Image pixel size is 0.5-feet GSD. Image type is natural color. Image horizontal accuracy is ASPRS Class 1 with limiting RMSE of 2.0 feet. Each file contains an image covering 2500 ft. by 2500 ft. on the ground. The coordinate system is Pennsylvania State Plane Coordinate System South Zone, North American Datum 1983."
In February 2006, this data was resampled from 0.5 foot to 0.15 meters and reprojected from NAD 83 State Plane Pennsylvania South FIPS 3702 (Feet) to NAD 83 UTM Zone 18N using the USGS Seamless Data Distribution System.