This part shall apply to any county having a metropolitan form of government and a population in excess of five hundred thousand (500,000), according to the 2000 federal census or any subsequent federal census. In addition, this part shall apply in any city having a population of not less than twenty seven thousand three hundred eighty (27,380) nor more than twenty seven thousand three hundred ninety (27,390), according to the 2000 federal census or any subsequent federal census. This part shall also apply in any city having a population of not less than twenty thousand nine hundred seventy (20,970) nor more than twenty thousand nine hundred eighty (20,980), according to the 2010 federal census or any subsequent federal census. In addition, this part applies in any city having a population of not less than fifteen thousand nine hundred (15,900) nor more than sixteen thousand (16,000), according to the 2010 federal census or any subsequent federal census, lying partly within a county with a metropolitan form of government and partly within an adjacent county.