Source / Outbreak map
The famous map published in 1855 marks cholera deaths by address around Broad Street in London and places those marks in relation to public water pumps.
The map made a spatial pattern visible, but it was one component of a larger case built from mortality returns, house-to-house inquiry, exceptions, water use, comparison, and an already-developed theory of transmission.
Reading the source
Street names, pumps, institutions, and stacks of short black bars reduce a complex neighbourhood to the features relevant to Snow's argument about a shared water source.
Each bar represents a death associated with a location rather than a moving person or complete life history. Their concentration around the Broad Street pump is visually forceful because the map joins civil registration to precise urban geography.
Snow asked why nearby populations, including a workhouse and brewery, recorded fewer deaths, and why some people farther away died. Separate water supplies and reported use of Broad Street water helped him interpret apparent exceptions.
Snow's case for waterborne cholera also drew on earlier outbreaks and mortality among households served by different London water companies. The Broad Street map communicates one local investigation, not the whole argument.
Making and myth
Snow suspected the pump before the familiar published map existed and persuaded parish authorities to remove its handle while the outbreak was already declining. The intervention did not by itself end the epidemic or immediately establish his theory among contemporaries.
The map contains deaths Snow could locate; it is not a complete population-rate map and does not show individual water consumption. Its apparent cluster requires the accompanying inquiries, text, and knowledge of who was exposed.
Later retellings often make Snow a solitary founder. Civil registrars, residents, parish officials, mapmakers, and the curate Henry Whitehead contributed records, testimony, local knowledge, and follow-up investigation on which the case depended.
Across the collection
Follow Snow's work on cholera and anaesthesia without reducing either field to a single heroic episode.
Place the Soho investigation within nineteenth-century epidemics, urban infrastructure, debate, and prevention.
Trace the broader development of population comparison, surveillance, field inquiry, causal argument, and intervention.