As shown by the official zoning map, the City is divided into 11 classes of districts. The boundaries of these districts are hereby established as shown on the official zoning map of the City, and said map and all notations, references and other information shown thereon shall be and are hereby made a part of this chapter by reference. The official zoning map, signed by the Mayor and properly attested by signature of the Clerk and date of adoption, shall be and remain on file in the office of the City Clerk.