Pennsylvania incorporates 2,559 municipalities, and the class each one belongs to is part of its legal name rather than a description. The Local Government Commission counts 1,454 second-class townships, 955 boroughs, 93 first-class townships, 56 cities and one town. That last figure is not a rounding artefact: Bloomsburg has been the Commonwealth's only incorporated town since 1870, and every other community is a borough, a township or a city. An address form whose locality label reads “City” mislabels the large majority of Pennsylvania addresses.
The practical hazard is that a borough and a township can carry the same name inside the same county while being separate governments with separate tax rates and separate records. Matching a place by name alone merges them. This is the same class of problem an independent city creates in Maryland or Virginia, except that Pennsylvania has it at the scale of a thousand-odd name pairs rather than a few dozen.
The postal side is unusually granular for the same reason. Pennsylvania holds 2,176 codes under 47 prefixes — more prefixes than any state except a small handful — and the principal place of a prefix is frequently a place most people outside the county have never heard of: 154 is Adah, 153 is Aleppo, 162 is Adrian, 160 is Boyers, 158 is Benezett, 178 is Beaver Springs. Those are boroughs and townships doing the work of naming a sorting area, and none of them is a city.
Meanwhile the cities the state is known for hold small prefixes. Harrisburg, the capital, anchors 171 with 26 codes, while 170 across the river at Camp Hill — a borough — is the largest prefix in the state at 92. Lancaster's 176 holds 11 codes, York's 174 holds 8, Allentown's 181 holds 8, and Philadelphia appears twice, as 191 with 81 codes and 192 with 2. A Pennsylvania fixture assembled from the five biggest cities will miss almost all of the state's postal structure; the address generator draws from the whole configured set instead.