Maps do not only describe the world; they are also used to change it. Governments draw lines that decide where houses can be built, where loans flow, where highways run and where waste is dumped. This level uses examples mainly from the United States, where the records are especially detailed.
Redlining
During the Great Depression the federal government created the Home Owners' Loan Corporation (HOLC) in 1933 to rescue homeowners facing foreclosure. Between 1935 and 1940 it produced "residential security" maps of more than 200 American cities, grading neighborhoods from A, colored green, to D, colored red and labeled "hazardous." Grades depended heavily on the race and ethnicity of residents, and neighborhoods with Black residents were almost always graded D, however solid their housing. Redlining is the practice of denying or limiting loans and services to areas judged risky, often on the basis of race.
Historians debate how much the HOLC maps themselves drove lending; the larger effect came from the Federal Housing Administration, created in 1934, whose underwriting rules discouraged lending in mixed or Black neighborhoods and favored new, white suburbs. Racially restrictive covenants written into property deeds barred sales to Black, Asian, Jewish and other buyers. In Shelley v. Kraemer (1948) the Supreme Court ruled that courts could not enforce such covenants, and the Fair Housing Act of 1968 banned discrimination in the sale, rental and financing of housing. But for decades families in redlined areas had been unable to buy or improve homes, the main way ordinary American families built wealth, and the gap passed to their children.
Zoning
Zoning is the division of land into districts where different uses and kinds of buildings are allowed. New York City adopted the first comprehensive zoning code in the United States in 1916. In Village of Euclid v. Ambler Realty Co. (1926), the Supreme Court upheld zoning as a legitimate use of government power, and the style of separating homes, shops and factories into distinct zones is still called Euclidean zoning. Defenders of zoning point to real benefits: it keeps a smelter from opening next to a school, protects green space and gives residents a say over change.
Zoning can also exclude. In Buchanan v. Warley (1917) the Supreme Court struck down openly racial zoning, but cities soon found other tools. Exclusionary zoning uses rules such as large minimum lot sizes or bans on apartments to keep out lower-income households. Because income and race are linked, such rules can preserve segregation without ever mentioning race. Large parts of many American cities are zoned for detached single-family houses only, which limits the supply of housing and pushes up prices. Critics from free-market economists to housing advocates argue that these rules make cities less affordable and less open. Defenders reply that neighbors deserve a voice in how their communities change. Some places have begun to loosen the rules: Minneapolis voted in 2018 to allow up to three homes on lots once limited to one, and Oregon passed a broader statewide law in 2019.
Environmental justice
Where pollution ends up is also a geographic question. In 1982 residents of Warren County, North Carolina, a mostly Black rural county, protested the dumping of soil contaminated with toxic chemicals called PCBs in a new landfill there, and more than 500 people were arrested. A 1987 report by the United Church of Christ, Toxic Wastes and Race in the United States, found that race was the strongest single factor associated with where hazardous waste facilities were located. Environmental justice is the principle that no group should bear an unfair share of environmental harm. Researchers still debate how much of the pattern comes from siting decisions and how much from poorer people moving to cheaper land near existing hazards. Either way, the burden falls on the same people.
Tools for fairer maps
Today geographic information systems (GIS) are computer tools that layer and analyze data tied to locations, such as income, flood risk, tree cover and bus routes. They can expose unequal treatment as clearly as the old maps imposed it.
Worked example: hotter streets
In 2020 researchers compared HOLC maps with satellite measurements of summer land surface temperature in 108 American cities. In most of them, neighborhoods once graded D were hotter than those graded A, by about 2.6 degrees Celsius on average and sometimes by much more. The reasons are geographic: formerly redlined areas tend to have fewer trees and parks and more pavement, highways and industrial land, all of which absorb heat by day and release it at night. Heat is one of the deadliest weather hazards, especially for older people and for those without air conditioning.
The case ties together every idea in this level. A map drawn in the 1930s shaped lending; lending shaped who could buy, repair and invest; zoning and highway decisions often followed the same lines; and nearly a century later the pattern shows up in the temperature of the air people breathe on a summer night. Many cities now use GIS maps like these to target tree planting and cooling centers, an attempt to use the tools of geography to undo some of the harm that geography once helped cause.