Mass. Gen. Laws ch. 54 § 2
Each city shall be divided into convenient voting precincts, designated by numbers or letters and containing not more than four thousand inhabitants. Every ward shall constitute a voting precinct by itself, or shall be divided into precincts containing as nearly as may be an equal number of inhabitants, consisting of compact and contiguous territory entirely within the ward, and bounded, so far as possible, by the center line of known streets or ways or by other well defined limits that constitute block boundaries recognized by the United States bureau of the census. If a ward constituting one precinct contains more than four thousand inhabitants, the aldermen shall divide it into two or more voting precincts. They may so divide a ward or precinct containing less than four thousand inhabitants. Except as provided in section one, when new precincts are established, the new division shall take effect on the thirty-first day of December following the making thereof.
Notwithstanding any authorization or requirement of this chapter, any precinct established or remaining unchanged following the decennial federal census shall remain unchanged for the purpose of forming congressional, representative, senatorial or councillor districts based on said census until the formation thereof as aforesaid, and if such precinct is within a ward the territory of which in such formation is included in two or more congressional, representative, senatorial or councillor districts, shall remain unchanged for the purpose of electing such officers so long as such districts are required by the constitution to be used for such purpose.
Mass. Gen. Laws ch. 54, § 2