REDWOOD CITY -- San Mateo County residents have until Sept. 20 to provide their own vision of the county's supervisorial districts.

The county is studying whether to shift the boundaries of its five districts as part of an upcoming switch from at-large to district elections. A nine-person District Lines Advisory Committee is expected Sept. 24 to choose one or more new maps for the Board of Supervisors to consider in October.

As part of its public outreach, the county has built a website where citizens can use an online tool to create their own supervisorial maps. The site has video tutorials explaining how to use the tool.

The committee is balancing several key factors in evaluating the maps, more than 20 of which have already been submitted. Among the considerations: the population of each district must be roughly the same; the voting power of minority communities must not be diluted; cities and communities with shared interests should be kept together where possible.

San Mateo County is the last California county to move to district elections, in which voters in each district pick their supervisor. Until now supervisors have been elected countywide. The change was prompted by a lawsuit, settled earlier this year, that claimed San Mateo County's at-large elections violated the rights of Latino and Asian voters.

For more information about the redistricting process, visit www.smcdistrictcommittee.org. To learn how to draw a map, go to www.smcdistrictlines.org.

Contact Aaron Kinney at 650-348-4357. Follow him at Twitter.com/kinneytimes.