Spatial Boundaries and the Local Context of Residential Segregation

Spatial boundaries are a defining feature of a city’s social and spatial organization. Rivers, highways, and train tracks create excess distance between nearby locations and often mark social separation – they become dividing lines that are well known to residents. Qualitative studies are rich with insight about the local significance of boundaries, but they have been largely ignored in the quantitative segregation literature. I advance existing scholarship by integrating spatial boundaries into the way we measure residential segregation for city populations. I introduce a new method that measures the proximity of residential locations and the reach of local environments around each location using road distance. This is more realistic than straight line ("as the crow flies") distance, because it captures the connectivity of roads and the distance imposed by physical boundaries. I measure segregation using the Divergence Index, which evaluates how surprising the composition of each local environment is given the overall population composition. I use this new approach to examine how spatial boundaries structure patterns of racial and ethnic residential segregation in several U.S. cities. I find that cities previously thought to have similar levels of segregation, nonetheless have different spatial patterns of segregation. Results reveal the salience of city boundaries in structuring segregation patterns in Detroit, and how the presence of physical boundaries affects the composition of local environments in Manhattan. Further, the experience of segregation is highly unequal within some cities, such as St. Louis. Some residents live in completely segregated environments, while others live in areas that are a microcosm of the city’s diverse population. In these cities of extremes, local segregation is both better and worse than indicated by the city’s overall segregation score. This research bridges qualitative insight on the local experience of segregation and how we measure segregation for city populations. My emphasis on spatial boundaries and local context reframes our understanding of segregated environments, and offers deeper insight into even the most studied U.S. cities.