\nDistricts shall be shown on a zoning map in a manner sufficient for identification. Such maps shall be part of zoning ordinances or by-laws. Assessors' or property plans may be used as the basis for zoning maps. If more than four sheets or plates are used for a zoning map, an index map showing districts in outline shall be part of the zoning map and of the zoning ordinance or by-law.
Massachusetts Legal Code