Said Director shall make the expense of such work chargeable upon the district in his opinion benefited by such work. In his said order declaring his intention he shall describe such district and declare it to be the district which will be benefited by such work. Such district may be described in such order by stating the exterior boundaries thereof, or by giving a description thereof according to any official or recorded map or maps, or by referring to the maps or block books customarily used by the Assessor and Tax Collector for City and County assessment or tax collection purposes, or by referring to a plat or map which shall be on file in the office of said Director at the time of making the order declaring his intention; said last mentioned plat or map shall indicate by a boundary line the extent of the territory included in the proposed district, and, if referred to as hereinabove provided for, shall govern for all details as to the extent of such assessment district.
When two or more public ways, not contiguous or directly connected, are to be improved under the same proceeding, such number of districts may be provided for therein as shall be deemed by said Director to be expedient.