The purpose of this dataset is to represent the Zip Code areas for the City of Philadelphia. The edges of Zip Codes are slightly modified for logical and cartographic purposes.
The arc layer contains data signifying information relating it to the polygon layer. It can tell you if both sides of the arc belong to one of the bounding polygons. All the arcs, including those with no boundary info, have naming attributes for labeling the polygon borders. Contact the Streets GIS unit for public consumption.