In unsubdivided land and where a zone boundary divides a lot, the location of such boundary, unless the same is indicated by dimensions shown on the map, shall be determined by the use of the scale appearing thereon.

Where a zone boundary line divides a lot in a single or joint ownership of record on February 14, 1972, the regulations for the less restricted portion of such lot shall extend not more than 30 feet into the more restricted portion; provided, however, that the lot must have frontage on a street in the less restricted zone.