Whose 1854 map of a Soho water pump founded epidemiology?

John Snow's. During a cholera outbreak that killed hundreds in a few days around Broad Street, he plotted each death on a street map and found them clustering around one public pump. He persuaded the parish to remove its handle.

The map is famous; the argument was better than the map. The outbreak was already declining when the handle came off, so that alone proves little. Snow's stronger evidence was the exceptions - a workhouse with its own well and almost no deaths, a brewery whose workers drank beer and were untouched, and a widow in Hampstead who died because she liked the taste of Broad Street water and had it delivered. He also ran a much larger study comparing two water companies serving intermingled houses, one drawing from a sewage-polluted stretch of the Thames.

He was not believed. The prevailing theory held that cholera spread through bad air, and the official report rejected his conclusion; the germ theory of disease was still years away and he had no organism to point at. He died in 1858 without seeing it accepted. The pump's contamination turned out to be a cesspit leaking a few feet away, into which a nappy from the outbreak's first victim had been emptied.