For the purposes of legislation and the regulation of a city's affairs, current cities of this Commonwealth as well as future cities shall be divided into four classes as follows:
(1) Cities of the first class, having a population of at least 1,000,000 inhabitants.
(2) Cities of the second class, having a population of at least 250,000 inhabitants but less than 1,000,000 inhabitants.
(3) Cities of the second class A, having a population of at least 80,000 inhabitants but less than 250,000 inhabitants on the date that the city adopts or amends a home rule charter designating it as a city of the second class A.
(4) Cities of the third class, having a population of less than 250,000 inhabitants other than cities of the second class A.