Redlines and Greenspace: The Relationship between Historical Redlining and 2010 Greenspace across the United States

Abstract

Introduction: Redlining, a racist mortgage appraisal practice of the 1930s, established and exacerbated racial residential segregation boundaries in the United States. Investment risk grades assigned $>80y$ ago through security maps from the Home Owners' Loan Corporation (HOLC) are associated with current sociodemographics and adverse health outcomes. We assessed whether historical HOLC investment grades are associated with 2010 greenspace, a health-promoting neighborhood resource.

Objectives: We compared 2010 normalized difference vegetation index (NDVI) across previous HOLC neighborhood grades using propensity score restriction and matching.

Methods: Security map shapefiles were downloaded from the Mapping Inequality Project. Neighborhood investment risk 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 NDVI for each HOLC neighborhood. Our main outcomes were 2010 annual average NDVI and summer NDVI. We assigned areal-apportioned 1940 census measures to each HOLC neighborhood. We used propensity score restriction, matching, and targeted maximum likelihood estimation to limit model extrapolation, reduce confounding, and estimate the association between HOLC grade and NDVI for the following comparisons: Grades B vs. A, C vs. B, and D vs. C.

Results: Across 102 urban areas (4,141 HOLC polygons), annual average $\pm \text{standard deviation}\left(\text{SD}\right)$ 2010 NDVI was 0.47 ($\pm 0.09$), 0.43 ($\pm 0.09$), 0.39 ($\pm 0.09$), and 0.36 ($\pm 0.10$) in Grades A-D, respectively. In analyses adjusted for current ecoregion and census region, 1940s census measures, and 1940s population density, annual average NDVI values in 2010 were estimated at $-0.039$ (95% CI: $-0.045$, $-0.034$), $-0.024$ (95% CI: $-0.030$, $-0.018$), and $-0.026$ (95% CI: $-0.037$, $-0.015$) for Grades B vs. A, C vs. B, and D vs. C, respectively, in the 1930s.

Discussion: Estimates adjusted for historical characteristics indicate that neighborhoods assigned worse HOLC grades in the 1930s are associated with reduced present-day greenspace. https://doi.org/10.1289/EHP7495.

Figure 1.

Nonrestricted propensity score distributions for 1940s U.S. Census tracts comparing HOLC better-graded tracts to worse-graded tracts. Propensity scores of the worse-graded group are shaded darker. (A) Propensity to be Grade B among Grades A and B HOLC neighborhoods; (B) propensity to be Grade C among Grades B and C HOLC neighborhoods; and (C) propensity to be Grade D among Grades C and D neighborhoods. Subsequent propensity score restriction cutoffs (1st and 99th percentiles) are indicated by the dashed lines. Note: HOLC, Home Owners’ Loan Corporation.

Figure 2.

Ecoregion-specific normalized difference vegetation index (NDVI) quintiles in all HOLC polygons across the Chicago, Los Angeles, and New York City urban areas. Images (A, C, E) in the left column are assigned HOLC grades. Images (B, D, F) in the right column are 2010 NDVI quintiles, with the deeper shade of blue indicating higher levels of greenness. (A) and (B) corresponds to the New York City metropolitan area. (C) and (D) corresponds to the Los Angeles metropolitan area. (E) and (F) corresponds to the Chicago metropolitan area. Note: HOLC, Home Owners’ Loan Corporation.

Figure 3.

Percentage of all HOLC polygons at a given mean annual 2010 NDVI stratified by HOLC grade. Note: HOLC, Home Owners’ Loan Corporation; NDVI, normalized difference vegetation index.