Zone boundaries, unless otherwise indicated, are lot lines or the center line of streets and alleys as shown on the official zoning map. Where the street layout actually on the ground varies from that shown on the zoning map, the designations shown on the map shall be applied to the streets as actually laid out so as to carry out the intent and purposes of this title. Where the location of the zone boundaries are shown on the zoning map to be other than street, alley, or lot lines, the depth of the zone shall be the same as that measured by scale on the official zoning map.