Redlines and greenspace: The relationship between historical redlining and 2010 greenspace across the United States

Abstract

Introduction: Redlining, a racially discriminatory mortgage appraisal practice in the latter half of the 1930s, established and exacerbated racial segregation boundaries. Investment risk grades, including redlining, assigned >80 years ago through Security Maps by the Home Owners’ Loan Corporation (HOLC) are associated with current socioeconomic factors, increased diesel exhaust production, hotter ambient temperatures, and adverse health outcomes. We sought to assess whether HOLC investment grades across the US are associated with recent measures of greenspace, a health-promoting neighborhood resource.Methods: We accessed Security Maps through the University of Richmond’s Mapping Inequality Project. Neighborhood investment grades included A (‘best’, green), B (blue), C (yellow), and D (‘hazardous’, red, i.e., redlined). We used 2010 satellite imagery to calculate the average normalized difference vegetation index (NDVI) for each HOLC neighborhood in four seasons. Our main outcomes were 2010 annual average NDVI and summer NDVI. We also assigned 1940 census measures to each HOLC neighborhood boundary using areal apportionment. To limit model extrapolation and reduce confounding, we used propensity score restriction and matching and compared HOLC grades as follows: grade B vs. A, C vs. B, and D vs. C.Results: Across the 71 cities from 24 states included in analyses, HOLC neighborhood annual average NDVI was 0.47 (SD=0.09), 0.042 (SD=0.09), 0.38 (SD=0.09), and 0.36 (SD=0.10) in grades A-D, respectively. In analyses adjusted for ecoregion, census region, and 1940s Census measures of socioeconomic status, HOLC grades B, C, and D were associated with 9.4% (95%CI:-10.8%,-8.0%), 5.7% (95%CI:-7.1,-4.3%), and 5.1% (95%CI:-7.9%,-2.2%) decreases in annual average NDVI compared to grade A, B, and C, respectively. Similar decrements were observed in summer.Discussion: Though redlining is now illegal, the institutional and structural racism outlined on Security Maps appears to persist. We observed that worse HOLC grade assignments in the 1930s were associated with reduced present day greenspace.