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 supervisorial districts shall be as nearly equal in population as may be and shall comply with the applicable provisions of Section 10301 of Title 52 of the United States Code, as amended. In establishing the boundaries of the supervisorial 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 supervisorial districts.