Streets and Highways Code § 5181

The district may be described by:

(a) Stating its exterior boundaries; or

(b) Giving a description thereof according to any official or recorded map; or

(c) Referring to a plat or map on file in the office of the clerk or engineer at the time of passing the resolution of intention, which shall indicate by a boundary line the extent of the territory included in the proposed district, and shall govern for all details as to the extent of the assessment district.