(a) The initial territorial limits of any municipality which adopts the mayor-council form of government as provided by this chapter shall be the same as under its former organization.
(b) If following a federal census of population or an alteration of the corporate limits, any council district shall contain a population of 10 percent more or less than the total population of the city divided by seven, then there shall be a reapportionment of the council districts in the manner hereinafter provided.
(1) The mayor shall, within six months after the publication of such federal census of population for the municipality or within six months after there shall have been such substantial change in the corporate limits of the municipality, file with the council a report containing a recommended plan for reapportionment of the council district boundaries to comply with the following specifications:
a. Each district shall be formed of contiguous and to the extent reasonably possible, compact territory, and its boundary lines shall be the centerlines of streets or other well-defined boundaries;
b. Each district shall contain as nearly as possible the same population, but not more than five percent more or less than the average.
(2) The council shall enact a redistricting ordinance within six months after receiving such report. If the council fails to enact the redistricting ordinance within the said six months, the redistricting plan submitted by the mayor shall become effective without enactment as if it were a duly enacted ordinance.
(3) Such redistricting ordinance shall not apply to any election held within six months after it becomes effective. No incumbent member of the council shall be deprived of his unexpired term of office because of such redistricting.