Cal. Pub. Util. Code § 28745.4

The board, in dividing the district into election districts, shall establish and define the boundaries of the nine election districts within the territory of the district, and shall number the election districts from 1 to 9, inclusive. The boundaries of the election districts shall be defined so that the districts shall be as nearly equal in population as practicable, considering the factors specified in Section 28745.6.