The portion of the cost of any improvement to be assessed against the property in a sewage or storm water facility improvement district shall be apportioned against such property in accordance with the benefits accruing thereto by reasons of such improvement. The cost may be assessed equally per front foot or per square foot against property within the district or by any other reasonable assessment plan determined by the governing body of any city with a population of three hundred fifty thousand or more inhabitants which is located in more than one county, or the governing body of the county of the first classification without a charter form of government that has a population of at least one hundred sixty thousand inhabitants, or the governing body of any county of the first classification without a charter form of government containing a portion of a city with a population of at least three hundred fifty thousand inhabitants, or the governing body of any county of the first classification without a charter form of government as of August 28, 1995, that has a population of more than one hundred five thousand but less than one hundred twenty thousand inhabitants, which results in imposing substantially equal burdens or share of the cost upon property similarly benefitted. The governing body of such city or county may from time to time determine and establish, by resolution, reasonable general classifications and formulae for the methods of assessing the benefits.