Elections Code Section 21500-21506
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.
21500.1. The board shall hold at least one public hearing on any proposal to adjust the boundaries of a district, prior to a public hearing at which the board votes to approve or defeat the proposal.
21501. The boundaries of the supervisorial districts shall be adjusted by the board before the first day of November of the year following the year in which each decennial federal census is taken. If the board fails to adjust the boundaries before the first day of November following the year in which the federal census is taken, a supervisorial redistricting commission shall do so before the 31st day of December of the same year. The adjustment of the district boundaries shall be immediately effective the same as if the act of the supervisorial redistricting commission were an ordinance of the board, subject, however, to the same provisions of referendum a apply to ordinances of the board.
21502. The supervisorial redistricting commission shall be composed of the district attorney, who shall be chairman, the county assessor, and the county elections official if he or she is elected by the qualified electors of the county, or, if not, the county superintendent of schools if he or she is elected by the qualified electors of the county, or, if not, the sheriff.
21503. At any time between the decennial adjustments of district boundaries, the board may cause a census of the county to be taken as provided in Section 26203 of the Government Code, and may adjust the boundaries of the supervisorial districts on the basis of that census, or on the basis of population estimates prepared by the State Department of Finance or the county planning department or planning commission, pursuant to Section 21500.
21504. Any person claiming that the estimates of population used in the redistricting pursuant to Section 21503 do not reflect the current population within the district boundaries more accurately than the most recent census data, may commence an action in the superior court in declaratory relief to determine that fact. The action shall be brought within 30 days after the adoption of the redistricting ordinance.
21505. The board may appoint a committee composed of residents of the county to study the matter of changing the boundaries of the supervisorial districts. The committee shall make its report to the board of its findings on the need for change of boundaries, and the recommended changes, within six months after the final population figures determined in each federal decennial census have been released, but in any event not later than August 1st of the year following the year in which the census is taken. Recommendations of the committee are advisory only.
21506. The term of office of any supervisor who has been elected and whose term of office has not expired shall not be affected by any change in the boundaries of the district from which he or she was elected.
At the first election for county supervisors in each county following adjustment of the boundaries of supervisorial districts, a supervisor shall be elected for each district under the readjusted district plan that has the same district number as a district whose incumbent's term is due to expire. A change in the boundaries of a supervisorial district shall not be made within 45 days before the first day for circulating nomination papers for an election of supervisors in the county or between the direct primary election and the general election.