Mass. Gen. Laws ch. 59 § 38
The assessors of each city and town shall at the time appointed therefor make a fair cash valuation of all the estate, real and personal, subject to taxation therein, and such determination shall be the assessed valuation of such estate. In cities, the assessors may, in any year, divide the city into convenient assessment districts.
The assessed valuation of real property subject to taxation under this chapter shall be classified as follows:--
Class one, residential;
Class two, open;
Class three, commercial, and
Class four, industrial.
The resulting amount shall be the taxable valuation of each class of property to which the assessors shall apply the tax rates applicable to each class as determined under section twenty-three A of chapter fifty-nine of the city or town, to determine the tax due and payable on such property.
Mass. Gen. Laws ch. 59, § 38