John Snow's London Cholera Map

John Snow is considered one of the fathers of modern epidemiology, in part because of his work in tracing the source of a cholera outbreak in Soho, London, in 1854.

The Broad Street cholera outbreak was a severe outbreak of cholera that occurred near Broad Street in the Soho district of London, England in 1854. This discovery came to influence public health and the construction of improved sanitation facilities beginning in the 19th century.

He plotted every death on a map with ingenious mapped bar charts and was able to show that the closer to the Broad Street water pump he plotted, the greater the number of deaths. The information helped convince the public a true sewage system was needed and spurred the city to action.