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La Representación Visual de Información
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A visit to John Snow's cholera-infected waterpump in London

On a walk early Saturday evening June 17 in London I visited the John Snow pub, which is mentioned in my account of the 1854 cholera epidemic in Visual Explanations, pp. 27-37. This is the site of the notorious wellhead pump that supplied the cholera-infected water that took the lives of 600 Londoners in September 1854. During that swift and terrible epidemic, Dr. John Snow did his brilliant streetcorner detective work (founding modern epidemiology), discovered the cause of the epidemic, and induced the Parish Council to remove the handle of the Broad Street pump, which ended the epidemic. It's more complicated than that, but the great contribution of John Snow was to identify the public health policy that ended cholera epidemics in England: keep the drinking water clean and free of sewage.

Here is a picture of the pub now and the sign with John Snow's portrait.

The friendly barman at the pub, Matthew, produced from a drawer under the bar what he described as the pump handle that John Snow had had removed to end the epidemic. My natural skepticism provoked the thought "Another relic of the true cross?" The handle is stamped and labeled by the UAB School of Public Health (University of Alabama in Birmingham?!) The UAB School of Public Health in Alabama has a publication called "The Handle," named after Snow's work. Here are pictures of the putative pump handle, which seems way too small to be a pump handle used by many people operating at the public well. It is likely a small-scale model of the real thing.

The above photograph of the souvenir handle in my hands was taken by my photographic assistants, engaged on the spot that Saturday evening at the JS pub. The photograph above was taken by my mate on the far right (holding the alleged pump handle); at far left, in this small world of endless coincidence, is a master's student in information design in London!

Below is a picture of a replica of the pump nearby and its accompanying rather battered plaque. Note the pivot pin on the pump, where the actual handle might have been, is quite large compared to the tiny pump handle in hand.

-- Edward Tufte

ET - Your visit to the bar now makes you eligible to be a member of the John Snow Society (the only membership requirement is visiting the John Snow Pub).


-- Daniel Meatte (email)

See the silhouette of the pump shown at the John Snow Society website along with the photograph of the pump above, which combine to indicate the pub's UAB souvenir handle is at about a one-quarter scale. The UAB should have put a scale of measurement on their tag; epidemiology is the not the place for dequantification.

-- ET

This link shows John Snow's famous map in a Flash-based viewer, centered on the Broad Street pump.

-- Matthew Bloch (email)

An interesting-looking book on the epidemic is out now in hardcover

The Ghost Map by Steven Johnson (At Amazon)

Amazon suggests "Beautiful Evidence" as a partner as well ;)

-- Stephen Hampshire (email)

Steven Shapin has written for the New Yorker a summary of Steven Johnson's The Ghost Map: The Story of London's Most Terrifying Epidemic—and How It Changed Science, Cities, and the Modern World (Riverhead).

-- Niels Olson (email)

i was happy to see that the map was included in the exhibit "London: A Life in Maps" which opened friday at the british museum (cf. http://www.bl.uk/londoninmaps )

-- cw (email)

Small update. I've just finished the "Ghost Map", and it is an excellent read. Highly recommended. ET gets name-checked a couple of times for introducing the map to the canon of infographics.

-- Stephen (email)

Just finished "The Ghost Map" and was disappointed that it was a book about a map with no map in it! (And I don't count the severely cropped chapter illustration on page 190 as a map.) Johnson spends a good part of a chapter effusing about the revised version of Snow's map (the one with the Voronoi diagram) but doesn't show it anywhere. I spent over an hour searching the internet without any luck, and even began thinking he didn't understand what he was describing, when I finally found a cropped version of the map buried in a PowerPoint presentation (how is that for irony?) - but I still haven't seen the full version anywhere else. There must be some lesson about visual explanations (or lack thereof) here!

Here is the PP presentation: http://www.epi.msu.edu/epi810/supersnow1%20M%209-6-04.ppt The slide with the map is #16 and you can see the faint dotted line representing equal walking distance (time) to the pump. Great concept that is poorly explained with just text.

-- John Hoffmann (email)

Who is sick - What would John Snow say?

This website is trying to provide a mechanism for basic
health data to pool into information by using Google Maps
to plot where (and when) people are sick.



From the website:

Who Is Sick was started in 2006 with a mission to provide current and local sickness information to the public - without the hassle of dealing with hospitals or doctors. With a strong belief in the power of people and a faith that user generated content can be extremely valuable, our team set out to create an entirely new system for tracking and monitoring sickness in your area and obtain sickness information. Information retrieved by tracking sickness in my area can also be used to map sickness trends in my region.

-- Tchad (email)

Dear ET,

I have been revising material on the Voronoi diagram (I have a 3D application in neuroscience that it fits quite nicely) and found a couple of mentions on the internet about John Snow using a Voroni map or diagram for his famous intervention in the London cholera outbreak, e.g. "A particularly notable use of a Voronoi diagram was the analysis of the 1854 cholera epidemic in London, in which physician John Snow determined a strong correlation of deaths with proximity to a particular (and infected) water pump on Broad Street." (http://mathworld.wolfram.com/VoronoiDiagram.html).

Do you know if this is true or just over enthusiastic revision of history?

Best wishes


-- Matt R (email)

Voronoi baloney

It's just a wrong guess.

-- Edward Tufte

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