Population and Housing Estimates for State Responsibility Area and CDF Direct Protection Area

The Fire and Resource Assessment Program (FRAP) of the California Department of Forestry and Fire Protection provides estimates of the number of people and housing units in State Responsibility Area (SRA) and in the California Department of Forestry and Fire Protection Direct Protection Area (CDF DPA). These numbers underestimate the actual number of people and housing units CDF protects because wildfires originating on CDF DPA have the potential to burn into adjacent, densely populated areas (Local Zone). 

Data Sources

click for population and housing estimates

Population/housing: Population and housing estimates are based on the 1990 post-census Tiger/line files from the U.S. Department of Commerce, Bureau of the Census. These data quantify population and housing by census block.

Census blocks vary in area. Within urban areas, they can be as small as a city block. At the other extreme, blocks can be thousands of acres in areas that are largely unpopulated public lands. For example, the figure at right shows the 4,146 census blocks for Mendocino County. The blocks become quite small in cities like Ukiah, but are very large in the portions of the county that are largely rural and dominated by public landholdings.

Housing units in the census data include traditional forms of housing and also teepees, caves, and other less conventional dwellings. Census blocks can extend offshore or include lakes to account for houseboats. It is important not to confuse the notion of housing units as used by the Census Bureau with structures, a term that does not always connote human residence.

Because the census data represent conditions in 1990, they do not portray post-1990 population changes. Nonetheless, the data provide a reliable source of spatially referenced population statistics, and are in common use by numerous public and private entities for a variety of purposes.

SRA/DPA: SRA consists of state and private lands (excluding areas of dense population and agricultural lands) for which the Board of Forestry has determined the state has financial responsibility to protect natural resources from wildfire (PRC 4125-4127). To consolidate areas of legal responsibility into larger blocks that can be more efficiently protected, CDF "swaps" portions of SRA protection responsibility with other agencies through the "balancing of protection" process. The resulting areas (CDF DPA) represent the land base for which CDF is the actual primary provider of fire protection services. Teale Data Center maintains digital spatial data for SRA and DPA on a continuous basis for the Department. For this exercise, FRAP used the July, 1995 version of the data.

Calculation Procedure

FRAP overlaid census block data with SRA and DPA data using a geographic information system (GIS) and apportioned the population in each census block to SRA and DPA lands.

For SRA, since a census block can include both public and private lands, the analysis assumes that only private (and Department of Defense) lands can be populated. For example, if a 100 acre census block has 5,000 people and it is 10% in private ownership, the 10 acres of private land are assumed to have all 5,000 people. If only 80% of this private land is actually SRA, the SRA population is assumed to be .8 x 5,000 = 4,000. The remaining 1,000 people are assumed to live within the remaining non-SRA private lands.

For DPA, if the DPA line splits the private lands in a census block, we apportion the population based on relative acreage. For example, if a census block has   5,000 people, and 60% of the private land is DPA, then the DPA population is 5,000 x .6 = 3,000. The remaining 2,000 people are assumed to live within non-DPA.

Contact Robin Marose at (916) 324-1646 or Robin.Marose@fire.ca.gov if you have any questions.

Last edited October 23, 2006 by Lauren McNees

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