Whenever a zoning lot is divided by the boundaries of an area as created by Section 109-03 (District Map) and as indicated on the District Map in Appendix A, the zoning lot shall be subject to the regulations of the area in which the greater portion of its frontage lies except that, in the case of any zoning lot having 15 feet or more frontage within Area A1 (Mulberry Street Regional Spine), the regulations of Area A1 shall apply to such zoning lot.