To learn what uses are permitted for properties in the city of Philadelphia, one would start by checking the base zoning district for a given property and cross-reference that zoning designation with the relevant section in the Philadelphia Code. A developer would also need to do a smidge more diligence to learn if the property is subject to one, or more, of the 33 additional overlay zoning districts that apply in combination with Philadelphia's base zoning districts. Overlay zoning districts impose additional requirements, restrictions and conditions, which can complicate development throughout the city.