London, September 1854. Soho is dying. 500 people dead from cholera in 10 days. Bodies piling up. Nobody knows why. Most doctors blame “bad air” - miasma theory. They think disease comes from foul-smelling vapors. They’re completely wrong. One doctor has a different idea. Dr. John Snow suspects the water. So he does something revolutionary: he makes a map. He marks every single cholera death on a street map of Soho. Dot by dot. Death by death. A pattern emerges. The deaths cluster around one location: the Broad Street water pump. He presents his evidence to local authorities. They’re skeptical. But they remove the pump handle anyway. The cholera outbreak stops. Almost immediately. Dr. Snow proved cholera spreads through contaminated water, not bad air. His map - this one map - changed medicine forever. It founded modern epidemiology. It created evidence-based public health. It showed the power of data visualization to save lives. Today, every COVID contact tracing map, every disease ou...