From spatial segregation to environmental inequalities: Mathematical and empirical evidence

Between-group spatial environmental inequalities arise from the uneven spatial distribution of social groups relative to environmental variables. Intuitively, if two groups shared identical spatial distributions, no spatial environmental inequalities would exist. This highlights the intrinsic link between spatial segregation and spatial environmental inequalities. Yet, despite this straightforward connection, few studies have scrutinized the theoretical and empirical relationships between these phenomena. To address this gap, we consider established measures and demonstrate mathematically that the level of spatial environmental inequality is bounded by the degree of spatial segregation. We then analyse boundary scenarios and identify two contrasting outcomes, depending on whether the environmental distribution aligns with or balances between the spatial patterns of the two groups. The added value of segregation-based environmental inequality indices compared to a standard inequality measure based on population-weighted mean differences is also pointed out. Empirical analyses of between-group spatial inequalities with respect to tree canopy cover in 97 French urban areas, covering 13 social groups, support these theoretical findings. Results show strong and significant correlations between segregation and spatial environmental inequality, accompanied by substantial heteroscedasticity and a clear boundary effect of segregation. The relationship varies by city size, being stronger and steeper in smaller agglomerations. Findings are robust across dissimilarity- and Gini-based formulations of spatial environmental inequality indices, as well as with a more standard inequality metric. • We establish a formal link between segregation and spatial environmental inequalities. • Segregation-based indices should be preferred to population-weighted mean differences. • Spatial environmental inequalities are bounded by the level of segregation. • Boundary scenarios reveal inequalities can be zero despite segregation. • Inequalities can exist despite uniform environmental distributions. • Empirical analysis in 97 French urban areas supports theoretical predictions.