After each decennial Census is completed, state and local governments must adjust their electoral districts to adapt to the results of the Census count.
California is one of several states that has an independent redistricting body - the California Citizens Redistricting Commission - responsible for determining congressional districts, state legislative districts and board of Equalization districts.
At the local level, the county is adjusting the Supervisorial districts, SMUD is shifting its Ward boundaries, and other local governments with by-district representation (like cities and school districts such as the San Juan Unified School District) are making similar modifications. Citizens are encouraged to participate in the redistricting process. That's appropriate considering we will be stuck with the new district boundaries for 10 years. Check out the pages herein for information on each redistricting process.