The Snow series is an educational course. We hope you will recognise our efforts by donating to TTE or becoming a paying subscriber, as writing the series took a lot of time and effort.

As Snow and his assistant were busy looking at water provision in South London, news reached him of a terrible cholera outbreak in the neighbourhood of Golden Square, Soho, central London. This had started in the night between 31 August and 1 September 1854. In the end, it would claim around 600 lives.

Golden Square was not far from Snow’s home on Sackville Street, and he rushed to the scene. He found a situation which he describes as reminiscent of Europe after the Black Death. Empty streets, boarded houses, and the few remaining people barricaded in their homes for fear of contracting cholera.

Scenery aside, this situation posed a real problem for Snow. It had characteristics similar to the Horsleydown outbreak and countless others he had collected data on, and he could reconstruct the denominator when the outbreak had subsided. It was relatively easy to find out how many lodgers lived and where in the neighbourhood because they either paid rent or owned their homes.    

The problem was different. The problem was finding a stable or credible numerator. Who lived where in the neighbourhood and died? Some would have died at home, sure. Others would have fled the place, had symptoms and died elsewhere; others would have been taken to the Middlesex and other local hospitals.

William Farr gave access to the death certificates, but Snow did his usual investigation. He knocked on doors and asked how many had been living in the house, how many were ill, and how many had died. After going door to door, he then visited nearby hospitals.

He could estimate the deaths as the epidemic abated and produced one of the most iconic maps ever. Ignoring the time being the denominator, he used what looks like a tourist plan of central London (but was made for Snow by the firm of Chaffins) and plotted all the pumps in the neighbourhood of Golden Square. Then, he drew a black bar for each death in each location and noticed a few peculiarities. 

He described the map thus: “Showing the deaths from cholera in Broad Street and the neighborhood 19th August – 30 September 1854. A black mark or bar for each death is placed in the situation of the house in which the fatal attack had ocurred”.

Here is his explanation of the map boundaries from On the Mode of Communication of Cholera. 2nd edition (MCC2):

To help with interpretation, here is a close-up of the Broad Street area from the same map:

To help him and his readers understand, he plotted the number of deaths in relation to the pumps in the area. But can you spot any other unusual features in the visual data?

The following picture is a reconstruction of the pump near the original spot in what is now Broadwick Street:

Note the missing handle or stirrup.

CONTEMPORARY THEMES

Snow’s was one of three maps of the outbreak drawn after it ended (see Lecture 18), but he was the only one showing all the pumps in the area. He could show the space outcome relationship because he was not encumbered by the baggage and obsession with certainty that Victorian and modern-day miasmatists carry.

Readings

Koch T. The Map as Intent: Variations on the Theme of John Snow. Cartographica 2004; 39(4). https://www.ph.ucla.edu/epi/snow/cartographica39(4)1_14_2004.pdf

Tufte, E.R. 1983. The Visual Display of Quantitative Information. Cheshire, CT: Graphics Press.