Where a district boundary line divides a lot other than by following a stream or street, which lot is single ownership at the time of the adoption of this Chapter or any district change, any use permitted in either district may be extended not more than 50 feet into the adjacent district, or to the boundary line of the divided lot, whichever is the lesser. A use permitted in the district so extended shall thereafter be a permitted use in the extended area. A property owner, however, shall be permitted only one election, after which the lot use shall be governed by the regulations of the district to which the portion of the lot shall have been annexed by such extension.