The classes of districts and certain combinations thereof designated in Chapter 18.08 may be established by ordinance insofar as the designations, locations, and boundaries thereof are set forth and indicated by written description, or in various sectional district maps which may hereafter be filed and adopted and which show such designations, locations and boundaries of certain said districts. Said maps and all notations, references, data, and other information shown thereon shall become a part of this title and subject thereto, and all such written descriptions and maps shall be designated as subsections of this section.