All land annexed to the City subsequent to the adoption of this Zoning Code shall remain subject to the previous township zoning district regulations until such time as the Zoning Map is amended according to the provisions of this Chapter and the Ohio Revised Code. All land annexed to the city which, prior to annexation, is not subject to township zoning shall remain unzoned until the Zoning Map is amended according to the provisions of this Chapter and the Ohio Revised Code.