Section 81H. Upon final action by the proper authorities in laying out, altering or relocating a public way, or in discontinuing the whole or any part thereof, or in establishing or enlarging a public park, or closing thereof in whole or in part, the lines and notations showing such improvement, discontinuance or closing, as so established or effected, shall, without further action by the city council or the town meeting, be made a part of the official map, if any, of the city or town in which such public way or park is located.