A post from Dan Fox, IMSL FSR and Analyst. From cholera, through Boris Bikes, to mobile phone photos: how London’s great infestations have been visualised
It’s a little unfair to compare a water-borne disease that causes deadly diarrhoea, to benign picture and bicycle sharing technologies. But just over 150 years apart, their analysis has benefitted greatly from effective data visualisation.
In the mid-19th century, action on the greatest public health challenges of the day was tragically handicapped by the widespread acceptance of miasma theory, which held that it was pollution in the air that was causing diseases such as cholera. Based on this, the London authorities would dump waste from cesspools into the Thames, believing they were removing the source of ‘bad air’ from population centres. Then, in August 1854, Soho was hit by an outbreak of Vibrio cholera that, within the month, had killed over 600 people. While germ theory (correctly positing micro-organisms as the true source of disease) was not yet widely understood or accepted, at least one man had already, some five years previously, started ruling out miasmic causes. In 1849, physician John Snow had published On the Mode of Communication of Cholera which began suggesting that it was all about something in the water. The rapid spread of cholera in Soho (which he described as “the most terrible…which ever occurred in this kingdom”) inspired further investigations by Snow. In 1855, he published a second edition of the article. Surveying local residents, Snow had revealed a concentration of cholera infections around Broad Street (now Broadwick Street), which he later transposed to a local map:
On proceeding to the spot, I found that nearly all the deaths had taken place within a short distance of the [Broad Street] pump. There were only ten deaths in houses situated decidedly nearer to another street-pump. In five of these cases the families of the deceased persons informed me that they always sent to the pump in Broad Street, as they preferred the water to that of the pumps which were nearer. In three other cases, the deceased were children who went to school near the pump in Broad Street. With regard to the deaths occurring in the locality belonging to the pump, there were 61 instances in which I was informed that the deceased persons used to drink the pump water from Broad Street, either constantly or occasionally.
The result of the inquiry, then, is that there has been no particular outbreak or prevalence of cholera in this part of London except among the persons who were in the habit of drinking the water of the above-mentioned pump well. I had an interview with the Board of Guardians of St James’s parish, on the evening of the 7th inst, and represented the above circumstances to them. In consequence of what I said, the handle of the pump was removed on the following day.
His map also highlighted a significant anomaly: the absence of cholera amongst the monks living next to the pump. When it was established that they drank only home-brewed beer, it added further weight to the water borne theory of the disease’s spread.
Snow’s work was the foundation of modern epidemiology and also partly inspired the crucial work of Joseph Bazalgette, building a modern sewerage system for London, from 1858. A century and a half later, and Londoners’ digestive systems are no longer as (ahem) fluid as in the days of cholera. Unfortunately, neither are our congested streets. The so-called ‘Boris Bikes’ aims to encourage commuters to make more journeys under pedal power, reducing pollution and freeing up road space. In the two years of their operation they have spread throughout Central London and into more suburban areas, with the total number of bikes due to rise to 11,000 in 2014. With the sheer volume of journeys (over 10 million in the first two years) and the quality of information pertaining to them (users, direction, distances, times), the data around Boris Bikes has been subject to a range of impressive visualisations. This mesmerising video from City University represents the density between the starting and end points of the first 5 million journeys:
Their rising and falling use throughout the day of a tube strike can be seen here.
And UCL’s CityDashboard displays the bikes’ real-time use and availability against other forms of transport, and useful information such as weather.
While the Mayor attempts to tackle our passage through London’s physical thoroughfares, the capacity of our virtual pathways, 3 (and now 4) G mobile networks, has been under increasing strain. Again, visualisation of the data helps us see the what, when and where of the problem. This photo compares the location of tweets (a few hundred bytes each) in the capital (the blue dots) to photographs (averaging about 1.3 MB from iPhones) posted to Flickr (red dots), and where they overlap (white dots).
In 2011, a BBC crowd-sourced project identified the extent of coverage throughout the UK, including coverage and data black-spots. In Sweden, the data visualisation of mobile phone use has been drilled down from the national, through the local, and into the personal with a billing app that helps identify personal peak times and most common connections.
Can all this information be interesting? Mostly. Are the visualisations pleasing? Certainly. But is it all of any actual use? In the right hands, definitely. Successful public policy is based on two elements: the successful modelling and simulation of a circumstance to correctly identify problems and their solutions; and communicating the extent of those problems and the necessity of the solutions to the public, upon whose consent and actions implementation relies. Would the commissioners of 19th century Soho have been so quick to remove the Broad Street pump handle, or the local residents so accepting of it, without the proof of it being the disease zero point on John Snow’s map? And wouldn’t local residents of the 21st century be happier, or at least more realistic, about permissions being granted for phone masts once they are better able to comprehend the trends in and threats to the use of mobile technologies in their vicinity?
Data visualisation has been a part of public policy ever since the mappa mundae were used to reinforce certain spiritual and geographical views of the world in the Middle Ages. Today, the technologies and skills are no longer in the hands of an educated and religious elite. They are available to anyone with a policy to make, a campaign to run, or a message to communicate.