When definite distances in feet are not shown on the zoning map, the district boundaries on the zoning map are intended to be along existing street, alley or property lines, or extensions of or from the same. When the location of a district boundary line is not otherwise determined, it shall be determined by the scale of the map measured from a given line.

Where the street layout actually on the ground varies from the street layout as shown on the zoning map, the board of adjustment may apply the designation shown on the mapped streets in such a way as to carry out the intent and purpose of the plan for the particular area in question.