Proportion of ground covered with impervious surfaces
Geographic Unit of Analysis:
|Percent of land area that is impervious (2011)|
|Financial District/South Beach||82.7%|
|Golden Gate Park||15.3%|
|South of Market||91.7%|
|West of Twin Peaks||56.4%|
According to the U.S. Environmental Protection Agency, "impervious or impermeable surfaces" are defined as surfaces that either do not allow, or allow only with great difficulty, the movement or passage of water. Between 2001 and 2011 the percent of land area in San Francisco that was deemed impervious was relatively constant - changing from 60.14% to 61.23%. The above map depicts the percent of impervious surface for every 30 meter by 30 meter square in San Francisco. The U.S. Geological Survey classifications for imperviousness values are: (1) developed open space (imperviousness < 20%), (2) low-intensity developed (20-49% imperviousness), (3) medium intensity developed (50-79%), and (4) high-intensity developed (imperviousness > 79%). Nine neighborhoods fall into the high-intensity developed category: South of Market, Chinatown, Tenderloin, Nob Hill, Mission, Mission Bay, Financial District/South Beach, Japantown, and Hayes Valley. The likelihood of storm water runoff in these neighborhoods is higher due to the high proportion of impervious surfaces. A majority of San Francisco neighborhoods fall into the medium intensity developed category, with a percent of impervious surface between 50 and 79. Only three neighborhoods, McLaren Parl, Golden Gate Park, and Lincoln Park have a percent of impervious surfaces at or below 20 percent, which allows for the increased absorption of rainfall and less runoff in these areas.
The National Land Cover Database 2011 Impervious Surface data was downloaded from the US Geological Survey Seamless Server and utilized for this analysis. The impervious surface data was opened in ArcGIS as a raster dataset and the zonal statistics spatial analysis tool was used to generate estimates of the average percent of impervious surface for each neighborhood.
The National Land Cover Database, Impervious Surface data is from 2011, therefore, new development in the city that has occurred since then may affect the ability of data to accurately illustrate present circumstances in San Francisco.
Impervious surface data was obtained from the US Geological Survey’s Seamless Server website at: http://seamless.usgs.gov/.
Environmental Protection Agency, Terms of Environment. http://www.epa.gov/OCEPAterms/