53 Pa. Stat. § 30656
In addition to powers heretofore granted to cities of the second class as provided for in an act, entitled "An act for the government of cities of the second class," approved the seventh day of March, one thousand nine hundred and one, and the supplements thereto, every city of the second class in its corporate capacity, in the interest of public health, safety, and general welfare, is authorized, by ordinance,
To regulate and limit the height and bulk of buildings hereafter erected or altered, and, for these purposes, to divide the city into districts, of such number, shape, and area as it may deem best suited to the purposes: Provided, That said regulations and limits shall be uniform for each class or grade of buildings throughout each district, and that the regulations in one or more districts may differ from those of other districts.
53 P.S. § 30656