Unless otherwise indicated by the zoning map, zone boundaries are lot lines, the centerlines of streets, and the centerlines of railroad rights-of-ways. If a zone boundary as shown on the map divides a lot between two zones, the entire lot shall be deemed to be in the zone, in which the greater area of the lot lies; provided, that this adjustment involves a distance not to exceed 20 feet from the mapped zone boundary. (Ord. 4128 (part), 1981; Ord. 3380 (part), 1968).