Mapping Disease: The John Snow Map of Cholera, Soho

By the time of the cholera outbreaks in 1830s and 1840s London, the streets of Soho had become a crowded slum that had gone down in the world, a world that Dickens’ Nicholas Nickleby found had the sort of back yards where trees would not grow, with:

 “… pieces of unreclaimed land, with the withered vegetation of the original brick-field. No man thinks of walking in this desolate place, or of turning it to any account. A few hampers, half-a-dozen broken bottles, and such-like rubbish, may be thrown there, when the tenant first moves in, but nothing more; and there they remain until he goes away again: the damp straw taking just as long to moulder as it thinks proper: and mingling with the scanty box, and stunted everbrowns, and broken flower-pots, that are scattered mournfully about – a prey to ‘blacks’ and dirt.”[i]

In fact, space syntax analysis of the built form shape and configuration of Soho and the surrounding areas found that the area was significantly more spatially segregated then the surrounding streets. This was linked to clear difference in urban form: shorter more numerous blocks and a complex morphology with with narrow visual fields, with the consequential effect that flows of movement into the area would have been restricted, creating a sense of a place separated from its prosperous surroundings, whether a locus of itinerant migrant workers, such as the seasonal Italian ice-cream sellers of the nineteenth century, radical revolutionaries at the turn of the twentieth century, or fashion sub-cultures in the twentieth and twenty-first centuries.[ii]

It was not until John Snow published the second edition of his essay ‘On the Mode and Communication of cholera’, showing the association between the incidence of deaths from cholera and the location of pumps in the Soho district of London, that a scientific use of mapped statistics was first established: to test hypotheses and to communicate the results (See the Broad Street map below).[iii]

London was among many large cities at the time that were suffering from periodic cholera epidemics from the 1830s onwards. Snow hypothesised that cholera was caused by a germ spread through contaminated water, rather than the prevalent ‘miasma’ theory of contagion through bad air. The two theories were debated vigorously, but Snow’s ground-breaking studies of the 1853-5 epidemic have made him to be considered the father of epidemiology not only due to his well-reasoned statistics, but due to his maps, which illustrated to a lay audience the evidence of a cluster of cholera cases amongst people living close to a single water pump on Broad Street and hence, that contaminated water was the source of the disease (see figure below showing a section of John Snow’s Broad Street map).

snippet_Soho_john snow

Section of ‘Street Map of Soho, around Golden Square, illustrating incidences of cholera deaths during the period of the Cholera Epidemic’. Image courtesy: The John Snow site (, Ralph R. Frerichs and the UCLA Department of Epidemiology

Notably, Snow did not use his map as a source of evidence, but as a way to communicate it. While some critique the mythology that surrounds the Snow story (which states that following his testimony, the handle of the pump believed to be the source of the disease was removed), Snow’s importance in the history of social mapping is profound. First, by establishing a clear spatial relationship between contaminated water and the disease and second, by using disease mapping as a way to observe, communicate and analyse statistics. Not only did he manage to disprove air theory as the cause of the disease, but he pinned down the statistics in such a way that his argument became immutable. In order to understand the results of his study in their full complexity the reader had to take in a mass of statistical tables, which, once read alongside the maps, became clear; whilst the clarity of the maps made them devices for communicating a simpler form of the argument to the general public.


A view of Union Place in Spitalfields Photograph: Horace Warner/The Religious Society of Friends in Britain

[i] Nicholas Nickleby, by Charles Dickens: Chapter 2.

[ii] L. Vaughan, “The Spatial Form of Poverty in Charles Booth’s London,” Progress in Planning: 67, no. 3 (2007).

[iii] John Snow, On the Mode of Communication of Cholera (London: John Churchill, 1855). The book, as well as a treasure trove of maps from Snow’s time as well as broader literature on the use of mapping in epidemiology can be found on the UCLA site, There was an additional map prepared for the local Parish Enquiry Committee, which has an additional dotted line to indicate the area within walking distance from the offending pump, see page 23 in Tom Koch and Ken Denike, “Essential, Illustrative, or… Just Propaganda? Rethinking John Snow’s Broad Street Map,” Cartographica: The International Journal for Geographic Information and Geovisualization 45, no. 1 (2010).

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