Descriptive Title:

Proportion of ground covered with impervious surfaces

Geographic Unit of Analysis:

Raster

Percent of land area that is impervious (2011)
NeighborhoodPercent
Bayview/Hunter's Point 71.4%
Bernal Heights 64.7%
Castro/Upper Market 65.3%
Chinatown 90.3%
Excelsior 70.7%
Financial District/South Beach 82.7%
Glen Park 42.9%
Golden Gate Park 15.3%
Haight Ashbury 65.3%
Hayes Valley 79.3%
Inner Richmond 74.1%
Inner Sunset 55.7%
Japantown 82.5%
Lakeshore 26.0%
Lincoln Park 12.4%
Lone Mountain/USF 72.9%
Marina 70.7%
McLaren Park 16.3%
Mission 85.5%
Mission Bay 84.2%
Nob Hill 86.9%
Noe Valley 65.8%
North Beach 77.0%
Oceanview/Merced/Ingleside 67.8%
Outer Mission 74.8%
Outer Richmond 71.5%
Pacific Heights 72.7%
Portola 71.9%
Potrero Hill 74.9%
Presidio 21.2%
Presidio Heights 74.0%
Russian Hill 77.7%
San Francisco 61.2%
Seacliff 52.8%
South of Market 91.7%
Sunset/Parkside 68.0%
Tenderloin 90.0%
Treasure Island 47.6%
Twin Peaks 39.3%
Visitacion Valley 67.7%
West of Twin Peaks 56.4%
Western Addition 75.5%

Why Is This An Indicator Of Health and Sustainability?

Pervious surfaces allow natural ground absorption of rainfall, replenishing groundwater tables and reducing the amount of storm-water runoff to the Bay. In turn, contaminant runoff to the Bay is reduced and residents swimming or fishing in the Bay have reduced exposure to oils, lead, and other toxins. In addition, pervious surfaces reduce sewage system loads by assimilating large amounts of rainwater. This reduces the potential for untreated sewage to be discharged, creating unsanitary conditions in the ocean and on the beach.

Interpretation and Geographic Equity Analysis

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.

Methods

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.

Limitations

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.

Data Source

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/

Detailed information regarding census data, geographic units of analysis, their definitions, and their boundaries can be found at the following links:

Interactive boundaries map

http://sfindicatorproject.org/resources/data_map_methods