Section 131. Within ninety days following receipt of an official notice which the city clerk shall send, within thirty days of the city election, to the city council notifying the said council that a new plan of city council organization or school committee organization, or both, has been approved by the voters, said council shall adopt an ordinance after public hearing providing for the division of the city into nine districts, or such other number of districts as may be specified in the question approved by the voters for the election of city council members or school committee members, as the case may be, by and from the voters of such districts at the next municipal election. In cities which adopt both a new plan of city council and a new plan of school committee organization the respective district lines shall be the same for both bodies. Each such district shall be compact and shall contain, as nearly as may be, an equal number of inhabitants, shall be composed of contiguous existing precincts, and shall be drawn with a view toward preserving the integrity of existing neighborhoods. Said districts shall continue in force until the next division of the city into wards required by section one of chapter fifty-four, at which time the city council shall divide the city into a number of wards equal to the number of said districts; and thereafter, upon the effective date of such wards for city primary, preliminary and general elections under said chapter fifty-four, such wards rather than districts shall be the units used for the election of those city council or school committee members who are not elected at large throughout the city. The city council shall adopt an ordinance providing for signature requirements for nomination papers for candidates for city council or school committee but in no event shall these requirements exceed two per cent of the vote cast in the preceding mayoral election in the respective district.