The Map that Shifted a Paradigm in Public Health

Dr. John Snow, who is credited with demonstrating the water-borne origin of cholera, first recognized the potential of applied cartography while mapping an outbreak of the disease in Victorian London in 1854. Dr. Snow, assisted by local community leader Reverend Henry Whitehead, dove straight into the heart of the epidemic, going door-to-door to conduct interviews and gather data points. In 1849, he published a controversial essay from his findings, ‘On the Mode of Communication of Cholera.’ In the essay, he directly challenged the established theories of disease transmission and stressed the importance of sewage-free water as a preventative measure against cholera. The second edition of this essay included his map of the distribution of deaths from cholera in the Broad Street district of London in 1854, with the Broad Street pump at the center of the map. Snow insisted that the handle of the pump be removed, and on September 8th, he finally succeeded. No new cases occurred after this date, proving that cholera was being spread directly through the water from the Broad Street pump. Not only did the process of mapping help lead to the development of his theory, but the map itself also inspired action with concrete medical results, marking a shift in the field of medical cartography as maps became more integrated into public health and the practice of medicine.


Over 150 years later, geography is still a major indicator of health status and driver of health disparities. In America today, your zip code is a better predictor of your health profile than your genetic code.  But despite that fact, geographic tools are extremely underutilized in the field of public health. Inspired by the lessons from Broad Street, we believe in leveraging the power of maps to visualize information, identify patterns, and make decisions.