Within thirty (30) days after the approval by the electors of the city of a proposition to adopt the modified mayor-council form of government, the governing body of the city shall, by ordinance, divide the city into four (4) districts to be numbered one (1) through four (4). Said districts shall be as nearly equal in population and as compact and contiguous as is practical. Dividing lines between districts shall follow precinct boundaries. In every eighth calendar year thereafter in the month of January, the governing body of the city shall adjust district boundaries to reflect approximately equal population.