Real or Secured Property Assesments
The California Constitution requires that all property be taxed, unless otherwise exempted under the California Constitution or United States Constitution. Article XIII-A of the California Constitution requires that real property be reappraised only when such property undergoes a change in ownership or has new construction (per Proposition 13).
The assessment roll, and tax bills, show land values and improvement values. "Improvements" include buildings or anything of a structural nature (such as swimming pools, paving, etc.). When you have an "improvement" value, it doesn't usually mean that you have recently "improved" your property.