Before Game of Thrones monopolized John Snows name, he was known among data journalists as the doctor who revolutionized how we look at data, maps, epidemics or microbes. When a cholera outbreak decimated the population of London in 1854, John Snow did something that no one before: he mapped the cases. Nowadays, it seems evident but it is only because John Snow showed the way. Before he created his revolutionary map, people believed that cholera spreads around by miasma in the air. Yet, his representation exposed that the death cases clustered around one particular water pump, and soon he was able to find the source of the devastating epidemic. In the end, it turned out that sewage from a nearby cesspit polluted the water for the pump; where someone dumped a babys nappy contaminated with cholera.

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