Cal. Elec. Code § 21500

Following each decennial federal census, and using that census as a basis, the board shall adjust the boundaries of any or all of the supervisorial districts of the county so that the districts shall be as nearly equal in population as may be and shall comply with the applicable provisions of Section 1973 of Title 42 of the United States Code, as amended. In establishing the boundaries of the districts the board may give consideration to the following factors: (a) topography, (b) geography, (c) cohesiveness, contiguity, integrity, and compactness of territory, and (d) community of interests of the districts.