The boundaries of various districts are shown on the zoning map accompanying and made a part of this code. The location of the boundaries shall be determined according to the following general rules of construction:
(a) Boundaries of districts shown along public streets and alleys shall be construed to be along the centerlines of such streets and alleys as they existed at the time of the adoption the map.
(b) Boundaries of districts shown to be located approximately along lot lines, shall be construed to be along the lot lines as they existed at the time of the adoption of the map.
(c) Boundaries within separate tracts and within unsubdivided property, shall be determined by use of the scale of the map.