Urban Heat Islands & Redlining Maps

The New York Times has mapped out how racist housing segregation in the United States, dating back to the Home Owners' Loan Corporation's Redlining maps, is a major contributory factor to the location of urban heat islands in towns and cities across the country.

Urban heat islands are areas of towns and cities which on days of extreme heat become unbearably hot. These areas can often become 10-20 degrees warmer than other areas in the same city. Urban heat islands tend to occur in the areas with the densest built environment and the most roads. This is a result of un-shaded roads and buildings absorbing heat and then radiating it out to their surroundings. The coolest places are usually neighborhoods with parks and lots of tree cover. The dark surfaces of roads and built materials, such as bricks and concrete, absorb more heat than grass and vegetation. Which is why the densest built areas tend to be significantly warmer than areas with tree cover or parks.

In How Decades of Racist Housing Policy Left Neighborhoods Sweltering the New York Times has created a story map which shows how across the United States neighborhoods which were redlined are usually the hottest parts of towns and neighborhoods which weren't redlined tend to be the coolest. The reason for this is that redlined neighborhoods have largely remained areas of deprivation and tend to have few trees and also a dense built environment. Non-redlined neighborhoods have remained mostly more affluent and are therefore more likely to have lots parks and lots of tree cover.



Of course because the HOLC redlining maps have had such an enduring effect on housing segregation in the United States these urban heat islands are often in neighborhoods with the largest black populations. The coolest neighborhoods tend to have large white populations.

Under President Franklin D. Roosevelt's New Deal black homeowners were discriminated against through the creation of redlining maps. These maps identified areas with significant black populations and labeled them as too high risk for mortgage support. Black homeowners living in these areas were therefore very unlikely to be successful when trying to refinance home mortgages from the government sponsored Home Owners' Loan Corporation.

Wenfei Xu has created an interactive mapping tool which allows you to compare the historical redlining maps side-by-side with modern day census data. The Redlining Map tool allows you to explore for yourself if the HOLC redlining maps have had a lasting impact on segregation in your city. Using the modern census data you can view the neighborhoods with a high percentage of black, white or Hispanic people and see if these areas correlate with areas which were deemed at risk or safe for lending purposes in the 1930's.



The HOLC map from the National Community Reinvestment Coalition also allows you to explore the lasting legacy of the HOLC's redlining maps. This interactive map allows you to compare modern data about income status and the racial mix of the population with the HOLC's historical redlining security ratings.

Using the HOLC map you can see if neighborhoods in your city with 'good' HOLC redlining ratings have remained largely white and wealthy or whether your city has become a beacon of social and racial equality. You can also use the National Community Reinvestment Coalition map to see where gentrification has occurred in a city. These are the neighborhoods which received the lowest HOLC redlining ratings but now don't have the stripes from the 'Low to Moderate Income' layer.