CHASM: A configurational measure of socio-spatial residential segregation

Despite recent advances in the quantification of residential segregation, several important limitations persist. Zone-based measures have low resolution and treat all locations inside a zone as identical; oversimplify the possibility of interaction between zones; and underestimate the role of the street layout and how it can shape potential movement and exposure. Here, we propose a new measure of socio-spatial residential segregation called CHASM that estimates potential exposure between different social groups based on their positions in the street grid and comparing them to a hypothetical scenario in which all groups are evenly distributed (i.e., a situation of non-segregation). Depending on the type of centrality chosen for the analysis, its scores represent the degree to which the distances of a street segment to the different social groups are unevenly distributed or, alternatively, the degree to which different social groups tend to avoid sharing the same street segments in their trips. We tested CHASM’s validity through a random permutation test in a hypothetical scenario and a comparison with more traditional measures in a medium-sized Brazilian city. The results suggest that CHASM is indeed able to quantify residential segregation and: (a) better estimates distances, connections, and continuities between different areas of the city, including the implications of barriers that are overlooked in zone-based measures; (b) minimizes distortions introduced by zones’ arbitrary shapes; and (c) opens up new possibilities for testing alternative designs for the street system.