1.3 The Power of Geographic Data

• Personal: you use a maps app to avoid traffic, or a family compares school ratings and commute times before choosing where to live.
• Business: a coffee chain studies census income data, traffic counts and competitors' locations before opening a store. Delivery companies plan routes with GPS data.
• Organizations: aid groups use satellite images to see where flooding hit hardest and where to send supplies.
• Government: cities use population projections to decide where to build schools, and countries use data to plan roads, hospitals and disaster response.

A census is an official count of everyone living in a country, usually with details like age, sex and household. The U.S. Constitution requires one every 10 years, and it has been taken every decade since 1790. The most recent was in 2020, and the next is due in 2030.

The census has big geographic effects. First, it is used for apportionment, which means dividing the House of Representatives' 435 seats among the states by population. After the 2020 census, Texas gained two seats; Colorado, Florida, Montana, North Carolina and Oregon gained one each; and California, Illinois, Michigan, New York, Ohio, Pennsylvania and West Virginia each lost one. That also shifted Electoral College votes, since each state's electors equal its House seats plus two.

Second, census data guides how trillions of dollars in federal funding are distributed for programs like Medicaid, highways and school lunches. Third, states use it to redraw voting districts (topic 4.6).

Satellite images let decision-makers watch change over large areas. Brazil's space research agency, INPE, has tracked Amazon deforestation with satellites since the late 1980s, and the data is used to target enforcement. Farmers use images of crop health to decide where to add water or fertilizer. After earthquakes or hurricanes, before-and-after images show which areas need help first.

Decisions are only as good as the data. If a group is undercounted, it can lose political representation and funding. The Census Bureau's own follow-up survey found that the 2020 census undercounted Black and Hispanic residents and young children. Data can also raise privacy concerns, since location data from phones can reveal where a person lives and works.

A classic local-scale example of data changing a decision comes from London in 1854. Physician John Snow traced cholera deaths in the Soho neighborhood to one water pump on Broad Street and convinced local officials to remove its handle. The map he published afterward, showing deaths clustered around that pump, became famous evidence that cholera spreads through contaminated water.