District lines must be drawn to ensure the five supervisorial districts are substantially equal in population. Under state law, population is determined based on the total population of residents of the County, as determined by the last Census. To the extent practicable, in accordance with the FAIRMAPS Act (AB 849), and as amended by AB 1276, district lines also must be adopted using the following criteria in the following order of priority:
- To the extent practicable, supervisorial districts must be geographically contiguous.
- To the extent practicable, the geographic integrity of any local neighborhood or local community of interest must be respected in a manner that minimizes its division.
- To the extent practicable, the geographic integrity of a city or census designated place must be respected in a manner that minimizes its division.
- Supervisorial district boundaries should be easily identifiable and understandable by residents. To the extent practicable, supervisorial districts must be bounded by natural and artificial barriers, by streets, or by the boundaries of the County.
- To the extent practicable, and where it does not conflict with the any of the above criteria, supervisorial districts must be drawn to encourage geographical compactness in a manner that nearby areas of population are not excluded from a district in favor of including more distant populations.
In addition, boundaries cannot be drawn for purposes of favoring or discriminating against any political party.