With their towering buildings, crowded streets, and tight-packed homes, modern cities often stand in stark contrast with their natural surroundings. However, scattered throughout almost every city are patches of green—parks, gardens, green roofs, and even urban forests. While it is widely accepted that these urban green spaces have value as visually appealing natural areas within cities, their contribution goes far beyond the aesthetic. Studies have linked proximity to green spaces with increased physical activity, decreased obesity, and better mental health. Green spaces also help mitigate the effects of urban heat islands and reduce air pollution. One study found that the air quality benefits from just a ten kilometer by ten kilometer urban green space can prevent two hospital admissions and two deaths per year.
The benefits of urban green spaces are staggering, but not everyone can take advantage of them. All over the world, a disproportionate number of residents in low-income and minority communities do not have access to green spaces and can’t reap their benefits. San Francisco has been applauded for its abundant and accessible green spaces—it was the first city in the United States to build a park within a ten-minute walk of every resident. In this "green" city, are green spaces equitably distributed?
The City of San Francisco provides data on the locations of its green spaces.
The city also publishes data on the percentage of non-white residents and the percentage of residents living below the poverty line in each neighborhood. Non-white residents are concentrated in the south and northeast, while residents in poverty are concentrated on the east side of the city.
Neighborhoods like Chinatown, which has many non-white residents, many residents in poverty, and little green space, and Marina, which has few non-white residents, few residents in poverty, and ample green space, suggest some inequity in green space allocation. However, neighborhoods like Bayview, which has many non-white residents and many residents in poverty, also has a large amount of green space. In general, there is little correlation between the percentage of non-white residents or residents living in poverty and the amount of green space in neighborhoods.
San Francisco's urban green spaces appear equitably distributed, but the benefits of a green space depend on more than just its area. Shade is a critical feature of urban green spaces, as it can limit the effects of urban heat islands. San Francisco publishes data on the amount of tree cover in each neighborhood, which can be used to estimate the amount of shade.
Chinatown and Marina, which both have little green space, also have little tree cover. However, Bayview, which has many residents in poverty and many non-white residents, has much green space but little tree cover, suggesting neighborhoods with more green space do not always have more shade. While green space was uncorrelated with poverty and non-white residents, neighborhoods with more residents in poverty and more non-white residents generally have less tree cover.
San Francisco also gives its parks a quality score from 0 to 100. It is possible that equitable distributions of green space area by neighborhood mask underlying trends in park quality just as they masked trends in tree cover. Mapping median park scores by neighborhood reveals that parks in northern neighborhoods tend to have higher scores than neighborhoods in the south.
Poverty appears to be a poor predictor of park score. However, neighborhoods with more non-white residents have lower median park scores. The Excelsior neighborhood, for example, has a low median park score and many non-white residents, but a roughly-average number of residents living in poverty.
These data suggest that San Francisco's green spaces are equitably distributed in terms of area. However, the percentage of tree cover in poor areas and areas with more non-white residents is lower than other neighborhoods, and the quality of parks is lower in areas with a higher proportion of non-white residents. This suggests an unjust distribution of shade and high quality green spaces within the city.