Correcting Myths in the Mapping of Cholera

Snow described which sewers emptied into certain rivers, how storms and floods could transfer contaminated water to cleaner sources, and how the spread of cholera was influenced by both time and place. In other words, the only map properly ascribed to John Snow alone was a mental map—a connecting of multiple data points and situations from which he could draw conclusions. It is that mental map, his piecing together of facts in relation to their spatial arrangement and knowledge of symptoms following a timeline of events, that led him to properly identify how cholera spread.

Snow examined water, met with patients and residents, and analyzed disparate patterns. He took these arguments to the city, who found them to be sound and well-documented. On September 8, 1854, the local council removed the pump on Broad Street.

This action may have slowed further spread of cholera in the area. But as Snow acknowledged in the aftermath of the initial outbreak, people leaving the city would have also caused such a decline in cholera as to be indistinguishable from the impact of closing the well.

The well was shuttered, cholera was in decline, and the famous map did not yet exist.

But others were already mapping the impact of cholera in their regions. In 1849, epidemiologist and physician Thomas Shapter published a book titled The History of Cholera in Exeter in 1832. The book leads with a map of cholera deaths in Exeter during the years 1832-1834. It shows buildings, yards, the River Exe, the locations of cholera deaths, where bodies were buried, and where clothes were burned. Charles Risdon is credited with the lithography.