London Cholera Outbreak, 1854

In 1854, a severe cholera outbreak struck the Soho district of London. At the time, most people believed that cholera was spread through the air. Dr. John Snow's map was able to spatially associate cholera cases with a single contaminated water pump. This led to three positive changes: the water pump was disabled, preventing further deaths, cholera was identified as a waterborne disease, and efforts began to improve water and waste systems in London. Shown here is the map created by Snow in 1854, as well as the same data represented with heat map symbology. The yellow part of the map represents the highest density of cholera cases and coincides with the Broad Street water pump.