The district boundaries are either streets or alleys unless otherwise shown and where the designation on the official Zoning Map indicates that the various districts are approximately bounded by a street or alley line, the center line of such street or alley shall be construed to be the district boundary line.

Where the district boundaries are not otherwise indicated and where the property has been or may hereafter be divided into blocks and lots, the district boundaries shall be construed to be lot lines, and where the designations on the official Zoning Map are approximately bounded by lot lines, said lot line shall be construed to be the boundary of the district.

In unsubdivided property, the district boundary lines shown on the official Zoning Map shall be determined by the use of the scale shown on such map.