Case study · Population health geography
When housing policy becomes a health map
Interactive map comparing 1930s HOLC redlining grades with CDC tract-level health estimates in the Minneapolis–St. Paul metro.
Health equity geography
Case study summary
- Problem
- Partners needed to demonstrate measurable present-day health differences tied to historical housing investment policy — not just cite the literature.
- Approach
- 1930s HOLC redlining grades spatially joined to modern census tracts and CDC PLACES model-based estimates, with an interactive public map and correlation chart.
- Result
- A public-facing tool comparing formerly redlined and highest-graded neighborhoods across diabetes, asthma, and mental distress in the Twin Cities metro.
Skills demonstrated
- Geospatial analysis
- Historical data integration
- Health equity framing
- Public dashboard design
- CDC open data
Tracts in view
866
225 overlap HOLC map areas
Gap: formerly redlined (D) vs. “Best” (A) tracts
Diabetes prevalence
+3.2% higher in D-grade areas
A-grade mean: 7.4% · D-grade mean: 10.6%
Interactive map
Choose a health metric to explore on the map and in the chart below. Switch the map layer between historical grades and today’s outcomes.
Correlation by HOLC grade
Among tracts overlapping 1930s HOLC map areas, mean diabetes prevalence rises from A-grade (“Best”) neighborhoods toward D-grade (“Hazardous”) areas. The gap between D and A tracts is 3.2%. This is an ecological pattern — not proof of causation — but it quantifies how historical housing policy still aligns with present-day burden.
Bars show mean tract-level prevalence for tracts assigned each HOLC grade (n noted below each bar). Tracts outside Minneapolis/St. Paul HOLC map coverage are excluded from this chart.
Why this matters
Redlining did not end with the maps — it shaped decades of disinvestment, segregation, and environmental exposure that persist in census-tract health patterns today. Linking archival housing policy data to modern small-area estimates is the kind of analysis public health departments, CHBs, and community organizations need when documenting structural drivers of disparity — not as rhetoric, but as measurable geography.
Stratum Health builds governed data products that connect historical context, administrative records, and modern health estimates — turning complex sources into geography and numbers partners can use in reports and programs.
Methods & data sources
HOLC redlining boundaries. Digitized polygons from the University of Richmond Digital Scholarship Lab, Mapping Inequality: Redlining in New Deal America (v3.4, accessed via GeoDa Center open data). Minneapolis and St. Paul city maps only. License: CC BY-NC-SA. dsl.richmond.edu/panorama/redlining
Present-day health estimates.
CDC PLACES: Local Data for Better Health, census tract GIS-friendly release (2025),
model-based BRFSS small-area estimates.
cdc.gov/places
· Dataset: yjkw-uj5s.
Life expectancy is not published at tract level in this PLACES release; only chronic-disease prevalence measures are mapped here.
Census tract boundaries. U.S. Census Bureau TIGER/Line 2020 census tracts (via Census TIGERweb services).
Spatial join. Each 2020 census tract in the Minneapolis–St. Paul metro was intersected with HOLC polygons. The assigned grade is the grade covering the largest share of tract area (area-weighted majority). Tracts with no HOLC overlap are shown without a grade. This is an ecological comparison — tract boundaries and neighborhoods have changed since the 1930s.
Gap statistic. Difference in mean tract-level prevalence between A-grade and D-grade tracts for the selected measure. Not adjusted for age, sex, or other covariates.