The proposed assessment district may be described in the ordinance of intention by stating the exterior boundaries thereof or by referring to the diagram provided for in the Preliminary report required therefor. The description of the maintenance shall be sufficient if the ordinance states in general terms the classes or kinds of maintenance contemplated, contains a general description of the property upon which the maintenance is to be done or the name by which such property is commonly known, and refers to plans and reports on file, if any, or such of them as may be suitable or proper for a description of the proposed maintenance. Portions of the improvement or of the territory comprising the assessment district need not be contiguous.