This is the original map of the Cholera Outbreak of 1854 as drawn by John Snow. I just finished reading The Ghost Map by Steven Johnson and the way he describes John Snow as being a revolutionary individual in the science of epidemiology made me want to investigate the original London 1854 Cholera outbreak map even further. Evidently what made Snow so unique during the outbreak of 1854 was his ability to focus on the tiniest of details (like the crack in the cesspool of 40 Broad St.) and then zoom way out to see macro trends like who was going where for their water. Aside from helping to end one of the deadliest outbreaks in a dense urban environment, he also began modern medical cartography (and data-viz) as we know it – overlaying different sets of data over the same map to spot trends.

What makes this map so special is that at the time it was drawn, the vast majority of people thought Cholera was transmitted by miasma – or foul air. The scattered dots (Cholera deaths) alone would seem to support this theory, but by simply adding the proximity to water pumps and then overlapping the streets to show how people traveled (on foot), one can clearly see that the Broad Street pump (marked with an “X” in the center of lots of the dots) might have had something to do with the outbreak. Its a swarm map and the pump is at the center.