[History by Numbers] The ghost map

How John Snow’s map of a London cholera outbreak ultimately changed the western world

Cholera would certainly have afflicted some of our ancestors’ lives – although it was written of in ancient times by Hippocrates, and was first discussed in a medical report in 1563, from 1817 to 1923 the world was stained by six overlapping pandemics of the disease. Even today, as part of a seventh pandemic which began in the 1960s, tens of thousands of people in the developing world die from it every year.

The major outbreaks in Britain in modern times were in 1832, when 55,000 people were killed as it spread out from London; in 1849, when more than 14,000 died in London alone and many people in Ireland, already weakened by famine, succumbed; in 1854, centred on Soho in London; and 1866, which saw localised outbreaks in the East End of London and Ystalfera in South Wales. The ‘Report on the mortality of cholera in England, 1848-49’ published by the General Register Office (you can find the whole report free at https://archive.org/details/b24751297) shows how widespread its reach was in England alone.

That report, compiled by the Registrar-General at the time, William Farr (1807–1883), discussed various theories on the cause and epidemiology of cholera, including ‘volcanic activity’, ‘fungus theory’, that it was ‘propagated by human intercourse’ and indeed Farr’s own favourite: the ‘miasma theory’ of bad air (which Farr thought was affected by the relative elevation above sea level).

The story of the man who got to the truth only a few years later is well-known enough, and he deserves to be another key figure in the canon of statistical pioneers whose work quietly changed our ancestors’ lives. His name was John Snow (1813–1858), commemorated to this day by an eponymous London pub a few yards from the epicentre of his research: the Broad Street water pump in Soho (now Broadwick Street).