Doctor John Snow’s cholera map of 1854 is often heralded as an example of how mapping can illuminate powerful insights on otherwise hidden patterns. Not so, writes Mark Monmonier in his excellent book on “Spying with Maps” which I just reviewed here.
Mark writes the following on John Snow’s famous map:
“If disease mapping has a poster child, it’s John Snow (1813-1858), the London anesthesiologist credited with discovering the water borne transmission of cholera. [...] Snow is best known for his 1854 map showing victims’ homes clustered around Soho’s infamous Broad Street Pump, which he identified as a source of contaminated water. According to epidemiological lore, the good doctor tried unsuccessfully to convince public officials to close down the pump.”
“Undaunted, he too matters in his own hands, removed the pump’s handle, and demonstrated the correctness of his theory when new cases plummeted. Truth be told, the epidemic had already run its course. What’s more, Snow made his famous dot map several months later, for a revised edition of his book on cholera transmission. Even so, his pin map continues to embellish discussions of GIS and disease.”
“Medical geographers, GIS experts, and some epidemiologists perpetuate the Snow myth because it promotes disease mapping as a discovery tool and enhances the stature of their own disciplines. But a careful examination of Snow’s writings indicates that he understood cholera’s mode of transmission well before he made the map.”
“Although Snow was a thoughtful observer, neither his map nor those of his rivals were of any value in generating insightful hypotheses. Snow’s famous cholera map was pure propaganda—and copycat propaganda at that—but proved eminently useful later in the century, when public officials needed convincing arguments to isolate drinking water from sewage.”
Although Mark is rightfully critical of Dr. John Snow’s legendary map, the last sentence above is quite insightful. The map, while unhelpful in knowledge discovery of cholera’s source, did become “eminently useful” to influence public health policy.