Designation of district boundaries. Boundaries indicated as approximately following the center line of streets, highways, alleys, railroad rights-of-way, streams, existing lot lines or municipal boundary lines shall be construed to follow such features indicated. Where boundaries are indicated as being approximately perpendicular to the right-of-way line of a street, highway or alley, such boundary shall be construed as being perpendicular thereto. Where a district boundary line does not follow such a line, position is shown on said Zoning Map by reference to an ordinance describing such lines or by specific dimension expressing its distance, in feet, from a street center line or other boundary line as indicated and running parallel thereto.