There’s a map, made more than 150 years ago using 1860 census data, that pops up periodically on the internet. On two yellowed, taped-together sheets of paper, the counties of the Southern U.S. are shaded to reflect the percentage of inhabitants who were enslaved at the time. Bolivar County, Mississippi, is nearly black on the map, with 86.7 printed on it. Greene County, Alabama: 76.5. Burke, Georgia: 70.6. The map is one of the first attempts to translate U.S. census data into cartographic form and is one of several maps of the era that tried to make sense of the deep divisions between North and South, slave states and free.1

But the reason the map resurfaces so frequently is not just its historical relevance. Rather, it’s because the shading so closely matches visualizations of many modern-day data sets. There is the stream of blue voters in counties on solidly red land in the 2016 presidential election, or differences in television viewing patterns. There’s research on the profound lack of economic mobility in some places, and on life expectancy at birth.

On major health metrics in the U.S., the shaded counties on the antebellum map still stand out today. Maps of the modern plagues of health disparities — rural hospital closings, medical provider shortages, poor education outcomes, poverty and mortality — all glow along this Southern corridor. (There are other hot spots, as well, most notably several Native American reservations.2) The region, known as the Black Belt, also features clearly on a new interactive created by FiveThirtyEight using mortality projectionsfrom researchers at the Institute for Health Metrics and Evaluation at the University of Washington. The projections show that, while mortality is declining nationally, including among those who live in the Black Belt, large disparities in outcomes still exist. Over the next several weeks, we’ll be looking at some of the causes of these disparities in the Black Belt and talking to the communities they affect.