When analysing the benefits of map-based spatial analysis projects, it is hard not to look at the case of John Snow’s map detailing the outbreak of cholera in the Soho district of London in 1854. Snow was a physician who lived on Berwick Street, near Broad Street, where the most cases of cholera occurred, and attempted to use the hypothesis of cholera being a water-borne disease to investigate how and where cholera was likely contracted. Using a detailed, pre-existing and detailed map of the Soho area, Snow recorded each individual death that was caused by cholera in the vicinity. Then, using the numerical data, Snow recorded interviews with the families of those who had contracted cholera but did not live in the epicentre of the disease on Broad Street. He found that many of the schoolchildren who had contracted the disease regularly drank from the pump on Broad Street on their daily walk to and from school. He also discovered after interviewing the workers in the brewery and the workhouse that they had their own water supply, negating the need to use the Broad Street pump. Snow also noticed that most of the seemingly random cholera deaths outside of the Broad Street area were caused because those affected had been in the area to tend to sick friends, and had consumed the water from the Broad Street pump during their time there. Using his map and the interviews conducted, Snow concluded that the cholera disease was being carried through the pump on Broad Street. When the pump was shut down by the local authorities, the cholera outbreak slowed, proving Snow’s theory to be correct.
This type of spatial analysis is important because, as Tom Koch points out, there is a difference between a mapper, such as Snow, and a map-maker (Koch, 7). The mapper uses the maps created to aid their findings in a broader study, as detailed in the John Snow case. A map-maker, on the other hand, creates a map as the final outcome of a project, meaning that the map is almost always influenced by the intentions of the map-maker. A mapper is often considered to be a physical geographer, who see maps as historical artefacts, compared to a map-maker, who understands maps at face value. Snow was considered one of the first people to use proximity as a measurement in analysing the intensity of a disease epidemic (Koch, 5); he was the first person to use analytical cartography in such a comprehensive fashion. His map is a densely-illustrated, extensive study, compared to a mapmaker’s finished product, which is never interested in a complex ecological portrait. John Snow’s use of cartography and spatial analysis is one of the first in contemporary map-based geographical information systems, which are used today to aid all manner of map-based investigations, such as concentration of gang-related crime, or larger-scale breaking down of class structures in a country, for example. Visual aids such as maps are used in a huge range of projects in modern research, and are integral to all spatial analysis.
Caitlyn Dempsey, ‘John Snow’s Cholera Map Using GIS Data (Web, 2013).
Tom Koch, ‘The Map and Intent: Variations on the Theme of John Snow’ in Cartographia, 39/4, (2004) pp. 1-14.