For the purposes of this ordinance, the City of Everett is hereby divided into 10 classes of districts, as follows:

The boundaries of each of these districts are hereby established as indicated on a map entitled “the Zoning Map” of the City of Everett, Massachusetts, dated February 1926, which accompanies and is hereby declared to be a part of this ordinance. These districts’ boundary lines are intended to follow lot lines as they existed at the time of passage of this ordinance, but where any such boundary line obviously does not follow such lot lines, it shall be deemed to be 100 feet back from the nearest street line it is drawn parallel to, unless otherwise dimensioned on the zoning map.