Not later than June 1, 1969, the then incumbent Council shall divide the Municipality into four (4) wards which shall be as nearly equal in population as is practicable. Every four (4) years after such first division, the Council shall review such division and when necessary shall adjust the boundaries of the four (4) wards so that following each such adjustment, the substantial equality in population of the four (4) wards shall be maintained. Each ward shall be composed of contiguous and compact territory as nearly quadrangular as possible, bounded by natural boundaries and street lines to the end that the population of each ward will have representation equal to that of each of the other three (3) wards in the government of the Municipality.