By mapping the clusters of cases, Snow discovered a concentration of incidents in around the intersection of Broad Street and Cambridge Street (now Lexington Street) where a water pump was located that drew water from the Thames. This led Snow to the conclusion that it was maybe a bad idea to offer up polluted river water as drinking water. And sure enough, when the pump was shut off and residents were directed to other nearby pumps, the incidences of cholera began to decline. The germ theory had proven to be true.

The first time I saw John Snow's map was in architecture school. Perhaps many of you have seen it as well. It is often used to illustrate the potential of visual representations to not only tell a story, but to teach the creator what that story actually is. In hindsight, it may seem obvious that polluted river water is something that we maybe shouldn't drink, but it wasn't at the time. This map helped people understand that. Today, we have far more sophisticated tools available to us, but we still have a lot to learn and we're doing that every day -- particularly during a pandemic.

One other thing worth mentioning is that there are a few exceptions to Snow's findings. Supposedly, many of the workers in a nearby brewery were able to completely avoid the cholera infection during the outbreak by only drinking their own brew. Some say it is because the brewery had its own water source, whereas others say it is because the brewing process -- the water is boiled -- kills the cholera bacteria. Either way, I think the moral of this story is pretty clear: when in doubt, choose beer over water.

Map: Wikipedia

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