The 12th Congressional District of California covers northern and central San Mateo County and the southwest part of San Francisco.

Under the provisions of the U.S. Constitution, legislation, and practice, the boundaries of congressional districts are drawn by the State legislature following the federal census which is taken every ten years. After the census, the number of Members of Congress allotted to each state is reallocated based on population. There are a total of 435 representatives in Congress, and that number remains constant. But since representatives are divided among states based on population, the number of representatives in Congress that each state receives can increase or decrease every decade. For example, following the 1990 census the number of representatives in Congress from California increased by 7 from 45 to 52, and following the 2000 census it increased by 1 from 52 to 53. California will continue to have 53 representatives in Congress until reapportionment following the census of 2010.

California, and every other state, is also required by the U.S. Constitution and U.S. law to redraw the political boundary lines for the state's congressional districts and also for the districts of the state assembly (house) and state senate. The boundaries must take into account the population shifts that are reflected in the census and adhere to established legal precedents. An average Congressional District in California has a population of 639,088 residents, and each district varies only minimally from this number.

The California legislature adopted legislation establishing congressional districts based on the 2000 census in 2001. Those changes are expected to remain in place until the 2012 election. Click here for a detailed map and demographic data for the 12th Congressional District. The U.S. Census Bureau also provides a map of the 12th Congressional District.

The 12th Congressional District includes the following areas:

• San Francisco - 17.7% of the residents of San Francisco. The areas of the city included in the district are in the southwest portion of the city, including areas around San Francisco State University. For a precise map of parts of the city in the 12th District, check this map
• San Mateo County - 90.9% of the residents of San Mateo County. The cities and unincorporated areas of San Mateo County that are included in the district are the following:
• Brisbane - 100%
• Broadmoor (unincorporated) - 100%
• Burlingame - 100%
• Colma - 100%
• Daly City - 100%
• El Granada (unincorporated) - 15.3%
• Emerald Lake Hills (unincorporated) - 100%
• Foster City - 100%
• Highlands-Baywood Park (unincorporated) - 100%
• Hillsborough - 100%
• Millbrae - 100%
• Montara (unincorporated) - 100%
• Moss Beach (unincorporated) - 100%
• Pacifica - 100%
• Redwood City - 29.9% (Redwood Shores and northern areas of the city)
• San Bruno - 100%
• San Carlos - 100%
• San Mateo - 100%
• South San Francisco - 100%

For demographic and other statistical information, click on this link to the U.S. Census Bureau Profile of the 12th Congressional District of California based on the 2000 Census.