The environmental neighborhoods of cities and their spatial extent

We define the new concept of an environmental neighborhood as the surrounding area influencing the environmental quality at a given point in a city, and propose a novel methodology to measure its spatial extent. We compute the spatial correlation of air quality and urban parameters from high spatial resolution datasets for New York City, where the urban characteristics are averaged over variable urban footprint sizes, ranging from 25 m × 5 m to 5000 m × 5000 m. The scale at which these correlations peak indicates the extent of the neighboring area that influences pollutant concentrations deviations from the city-wide average. The results indicate that the scale of these environmental neighborhoods ranges from ∼1000 m (for attributes such as road area or building footmark) down to ∼200 m (for building use or green area). Selecting this optimal neighborhood scale is thus critical for identifying the urban fabric and activity attributes that have the largest influence on air quality; smaller footprints do not contain all the pertinent urban surface information while larger footprints contain irrelevant, potentially misleading information. The quantification of this scale of influence therefore enables more effective and localized policies and interventions to improve urban environmental quality and reduce urban health disparities. More broadly, the findings indicate that, in a wide range of environmental and ecological applications where surface heterogeneity is a primary driver, the scale of analysis is not an external parameter to be chosen, but rather an internal parameter dictated by the problem physics.