Data design: The genius of Jon Snow

March 23, 2009 at 4:28 pm

I recently finished reading Steven Johnson's The Ghost Map, which is an incredible book on the Cholera outbreak in London's Soho district in 1854. One wouldn't naturally associate violent intestinal disease in Victorian London as a great source of design inspiration, but not only did this dark chapter in London's history produce a fantastic data visualisation model, it also changed the model of how all urban environments exist to this day.

In 1854 London was the biggest city the world had ever seen, and was literally drowning in its own filth. There was no sewage system in place and those that lived in the capital literally threw their waste and cesspits out into the crowded streets and river Thames. As you can imagine, as a result, London was a disgustingly smelly place to be and was periodically engulfed by disease - most notably Cholera. To give you a little insight into the appalling conditions London's inhabitants had to endure, the following extract is from the social historian Henry Mayhew, who wrote the following for the Morning Chronicle in 1849:

As we passed along the reeking banks of the sewer the sun shone upon a narrow slip of the water. In the bright light it appeared the colour of strong green tea, and positively looked as solid as black marble in the shadow - indeed it was more like watery mud than muddy water; and yet we were assured this was the only water the wretched inhabitants had to drink.

As we gazed in horror at it, we saw drains and sewers emptying their filthy contents into it; we saw a whole tier of doorless privies in the open road, common to men and women, built over it; we heard bucket after bucket of filth splash into it, and the limbs of the vagrant boys bathing in it seemed by pure force of contrast, white as marble.

Largely owing to the wretched stench and the appalling conditions of the day, some of the greatest minds of the nineteenth century collectively made possibly one of the greatest mistakes in the history of science and medicine; they were all convinced that the smell of London was causing people to become sick; it became known as the Miasma theory of disease. Sir Edwin Chadwick, who was a notable social reformer, responsible for the passage of the Public Health act of the day, said in his book on 19th Century social reform:

All smell is, if it be intense, immediate acute disease; and eventually we may say that, by depressing the system and rendering is susceptible to the action of other causes, all smell is disease

With such appalling living conditions it is no surprise that Cholera reared its ugly head periodically and swept through the city of London. The start of the deadly 1854 outbreak of cholera happened on August the 18th, where a popular water pump at 40 Broad Street (now Broadwick Street) got infected with Cholera. Over the following 10 days Cholera literally decimated the population of Soho; 10% of the neighbourhood died - entire families were wiped out within a 24 hour period!

This is where the brilliance of Dr. Jon Snow effectively changed the shape of how we approach disease and how all modern urban environments exist to this day. By 1854, Jon Snow had already revolutionised surgical procedures by discovering chloroform for controlled anesthesia, and was literally into a million different things - in this sense he was a classic Victorian dabbler. Snow was also a staunch skeptic of the Miasma theory of smell causing disease. Snow actually brought a water borne theory of Cholera to the health authorities several years before, in his 1849 essay On the Mode of Communication of Cholera, but couldn't convince anybody of its merit, thus it was largely ignored.

Given that Snow was convinced that Cholera was a waterborne virus it didn't take him very long to use the horrendous 1854 outbreak of Cholera as an opportunity to prove his theory once and for all. Snow was a Soho local and he very quickly determined where the deaths were clustered together - they all pointed towards the pump at 40 Broad Street. However, so blinkered were the Miasmatists, Snow knew that he was going to have to use more than just numbers to justify his theory. Snow ultimately did this by designing his now infamous map, pictured below, that is simply exquisite in its execution.

There are a number of exceptional about this map. The idea is that each bar represents a death from Cholera. The concentration around the pump at 40 Broad Street clearly shows more deaths and it trails off the further out from the pump you are. This is clearly a huge part of the communication piece of the map; that something terribly bad has happened in the vicinity of the pump. People tend to focus on this part of the map, and it is clearly an overwhelming piece of visual communication, however, that wasn't the most original or convincing part of it. The thing that Snow did that was really clever, and ultimately much more convincing in changing opinions, is the line around the vicinity of the pump; this is an attempt to represent time geographically. This line is the space that puts people within it closer, in terms of journey time, to the pump at 40 Broad than any other neighbouring pump. Every space inside that area illustrates an intense concentration of death from Cholera.

Owing to Snow's brilliant map, the authorities finally accepted the theory of Cholera being water borne and they removed the handle of the pump and it ultimately stopped the spread of the disease in 1854. It also paved the way for a sewage and sanitation systems to be put in place; one of the greatest engineering feats to be undertaken in London's history; changing the way that urban systems exist and continue to grow to this day.

So what can we take from Snow's brilliance in communicating critical information in his design? Well, what Jon Snow did was simply communicate the essential material in his story of the Cholera outbreak being waterborne. He agrressively edited the data that wasn't adding to the story of a pump killing hundreds of people. Snow only included information that painted a crystal clear picture that the pump at 40 Broad Street was the sole cause of the Cholera outbreak. He did an outstanding job.

I visited Broad Street (which has since been renamed to Broadwick Street) recently and sadly there isn't much left on the street that existed in Snow's day. There is thankfully a water pump with its handle removed (not the actual one unfortunately) as a memorial for both the people that died and the brilliance of Jon Snow's work on that hot summer over 150 years ago. There's also a pub too, that I believe is the only structure on the street that existed in Snow's day; legend also has it that the original pump handle that was removed still sits behind the bar of the pub, but nobody really believes it. And the pub's name? It's called The John Snow, thus his legacy lives on.

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