The new Contra Costa County supervisorial district map will likely move Diablo, Blackhawk and the Camino Tassajara area from District 3 Supervisor Diane Burgis’ purview to that of District 2 Supervisor Candace Andersen.

With one more public hearing scheduled before making a final decision, the board Tuesday unanimously endorsed a tentative map expanding Anderson’s reach to the east, placing the three Tri-Valley communities into the same district as Danville and San Ramon — cities with which they are already largely associated based on geography and demographics.

Political districts get re-drawn every 10 years, after the census results are released. The 2020 Census showed Contra Costa County growing by 11.35 percent since 2010, from 1,049,025 in 2010 to 1,168,064 residents in 2020.

The biggest gain was in Burgis’ District 3, with an additional 36,560 residents, an area covering much of Antioch, Oakley, Brentwood, and unincorporated East County.

The least amount of growth occurred in supervisor Karen Mitchoff’s District 4 (10,442 residents), an area covering Concord, Walnut Creek, Pleasant Hill and Clayton.

The goal is to create districts as equal in population as possible, while meeting all federal and state legal guidelines, such as respecting geographic integrity of an area, or a census-designated place, or local community of interest.

Under the new plan, all of Pinole would be in supervisor John Gioia’s District 1. Pittsburg’s Tuscany Meadows moves to supervisor Federal Glover’s District 5, with Antioch split at Somersville Road and Auto Center Drive, up Railroad Avenue.

Morgan Territory Road area inside the Mt. Diablo School District would move to District 4. Concord would be split at the former railroad right-of-way and highways 4 and 242. District 2 would now extend through Tilden Park, almost to Kensington. Walnut Creek would split between districts 4 and 2 at Highway 24 and Interstate 680. The Saranap and Castle Hill areas would be in District 2.

The board will hold one more public hearing Nov. 23, before voting on a final map the same day. The state deadline for redistricting is Dec. 15.