Property Assessment Tool: Data Notes


Notes on the Data



Certain condominiums aren't included on the map, and the difference seems to be between condos owned by a single firm or by multiple owners.  In the former, a building ID is tagged to a single entry of assessment.

Issue with Categorizing Properties

While categories exist for each assessment, the "Residential" classification of properties applies to both townhouses and single family residences.

San Francisco

Proposition 13

Passed in 1978 for the state of California, Proposition 13 "replaced the practice of annually assessing property at market value with a system based on cost at acquisition". Essentially, properties are assessed upon change of ownership, and as long as the properties are not sold, future increases are limited to 2%.  Read more here.

For the visualization, this means that it's difficult to visually compare market assessments like it would for Vancouver or Edmonton where assessments occur more regularly.  Two similar properties that are just beside one another could have wildly different assessment values (like $1M vs $70k) because the one with a higher assessment was sold in the past year, as opposed to the other which hasn't had a change in ownership since 1975.

Derived Assessment Value

The shown assessment value is derived from the open data this way:

  • Closed Roll Assessed Improvement Value
    + Closed Roll Assessed Land Value
    - Closed Roll Misc Exemption Value
    - Closed Roll Homeowner Exemption Value = Assessment Value in Tool


Multi-unit Properties/Condos

Where multiple assessments are provided for a given identifier ("LAND_COORDINATE"), the land and improvement values for all the assessments are summed.  

Issue with Categorizing Properties

The data doesn't have a clear way to categorize properties. There's a "ZONE_CATEGORY" attribute that shows promise because the values include "One Family Dwelling", but it appears the categorization applies to properties in a zone, not a property itself.  Golf courses, schools, and parks, including Stanley Park, share the same category as single family homes.