The boundaries of land zones shall be determined and defined or redefined from time to time by the adoption of zone maps covering the city, showing the geographical area and location of the zones. The zone map or maps shall be, upon its final adoption, a part of this title, and the map, and all notations, references and other information shown thereon, thereafter shall be as much a part of this title as though all matters and information set forth on the map were fully described in this chapter.