Wherever a Front Yard is required for a Lot facing on a Street for which a Subdivision plat has been recorded in the office of the Salt Lake County Recorder, the depth of such Front Yard shall be measured from the mapped Street line provided by the Subdivision plat. Where a Subdivision plat has not been recorded and no widening is anticipated in the Major Street Plan, measurements shall be made from the existing Right-of-way line. Where widening is anticipated in the Major Street Plan, measurements shall be made from the proposed Right-of-way line.