After the publication of a federal census of population or a substantial change in the corporate limits, if any council district contains a population which is 10 percent more or less than the total population of the city divided by the number of council districts, then the council shall redistrict the boundaries in the following manner:
(1) Within six months after the publication of such a census or after such a change in the corporate limits, the mayor shall file with the council a report recommending a plan for redistricting of the boundaries in accordance with the following standards:
a. Each district shall be formed of contiguous and, to the extent reasonably possible, compact territory, and its boundary lines shall be the center lines of streets or other well-defined boundaries;
b. Each district shall contain as nearly as possible the same population, but shall not vary by more than five percent from the average.
(2) The council shall enact a redistricting ordinance within six months after receiving such report. If the council fails to enact a redistricting ordinance within that period, the redistricting plan submitted by the mayor shall automatically become effective, without any action by the council, as if it were a duly adopted ordinance.
(3) No redistricting ordinance shall apply to any election held within six months after it becomes effective. No new district boundary shall become effective until the next regular municipal election. No term of an incumbent member of the council shall be shortened because of any redistricting.