When a city or other local government agency embarks on a public works project — such as a new road or a sewer system upgrade — it may form an assessment district to raise the funds needed to cover the expense. An assessment district is a specially designated area encompassing properties that stand to benefit from a particular improvement.

If you are a homeowner in one of these areas, you and your neighbors will collectively pay in proportion to your share of benefits received. Usually, your proximity to the improvement and the size of your lot will determine the amount you owe. The resulting assessment will appear as part of your property tax bill. Expect to see these additional special taxes over the course of several years, as you are actually repaying bonds sold by the government to finance the project. Since the life of a bond issue is an average of 15 to 20 years, don't expect that the special assessment will disappear quickly. Thanks to Proposition 218, however, California State law now requires that property owners who would benefit from a public improvement — and thus pay for it — approve the creation of the assessment district.

For details on special taxes affecting your property, look at the part of your tax bill labeled "Direct Charges and/or Special Assessments." There, you'll find the code, agency name, and phone number relating to any additional taxes on your bill. If you have questions, you can simply call the agency responsible for the special assessment.

In its Property Zone section, the Web site of the City and County of San Francisco, Office of the Treasurer & Tax Collector, also offers comprehensive information. Here, you can find a number of useful resources for homeowners, including a "Property Tax Calendar" and detailed information on "How to Read Your Property Tax Bill." You can also view and pay your property tax bill online at the Office of the Treasurer & Tax Collector, Property Tax Information & Payment section.