The legislative body shall also generally define the boundaries or extent of the district or lands to be specially assessed to pay all or any part of the cost of the proposed improvement or acquisition.
The district may be described by:
(a)
Stating the exterior boundaries thereof, or
(b)
Giving a description thereof according to any official or recorded map or maps, or
(c)
Referring to a plat or map on file in the office of the clerk of the legislative body which shall indicate by a boundary line the territory to be included in the assessment district, and which shall govern for all details as to the extent of the district.