Digitally Mapping the Spread of Epidemics

Today, we are surrounded by maps. GPS makes directions much easier, whether it is for long road trips or just meeting people somewhere you have never been before. (I have a horrible sense of direction, and am always very glad when GPS can point me in the right direction, even with any flaws.) Aside from geographical maps, infographics float around the web in different forms. These depict relative sizes of countries; demographics; people’s perceptions of countries and many more. Susan Schulten’s work discusses the development of the second type of map in the United States during the 19th century. She explains how governments drowning in new statistics from multiple sources began to organize all this information into images, thus allowing patterns to form in ways that would not be seen if the information was left in text form. Advances in printing and lithography allowed for these maps to be published and edited cheaply, giving a boost to the new industry. New sources such as census and climate data were used to predict weather patterns and plot demographics. Schulten’s blog on 11of the most influential infographics of the 19th century provides a few examples of these types of maps. One shows the distribution of religions, another the origins of residents, and another the average precipitation across the country.

The type of map I am most interested in is not on this list, but is mentioned in Schulten’s book, Mapping the Nation. In her chapter on "Disease, Expansion and the Rise of Environmental Mapping," she discusses how doctors, and other medical professionals of the 19^th century began developing maps to help them explain the spread of epidemic diseases. To understand the full importance of these maps, we need to understand the debate that raged over the causes of epidemic diseases. On one side was the then reigning concept of miasma theory, in which diseases were caused by bad air. And on the other side was the current concept of germ theory, in which diseases are caused by microscopic organisms. Up to the mid-19^th century, miasma theory held sway, with most doctors dismissing germ theory as false. While polluted air can cause disease, it is only half the puzzle, or in other words a cause of disease, but not the right cause for the disease being examined. Schulten argues that medical maps were useful in this context because they provided a method to plot out outbreaks and search for their causes. She explains how these maps often stressed environmental factors, which strengthened belief in miasma theory. American examples include the Brigham map, which depicted how cholera followed trade routes, while another focused on the statistics of outbreaks. The most famous of these maps was by a British doctor, John Snow. His map used statistics from household deaths, streets, and drinking water to trace cases of cholera back to a single pump in Broad Street. His map linked the spread of the disease specifically to the water from that pump and helped prove the validity of germ theory over miasma theory.

 Snow's Cholera Map

Image taken from Wikimedia Commons

Digital mapping tools offer a range of options to enhance Snow’s and other medical maps for interpretation. Miriam Posner's blog provides links to instructions on how to develop these types of projects. The map itself could be made into part of an online gallery, with the addition of any available images or texts from the era to contextualize the period. Wider issues involving city planning and public health initiatives could also be discussed. With more research on the spread of the disease, a time-lapse map could be developed to illustrate how fast the disease spread from its epicenters. Maps could also be overlaid onto modern day maps to show the differences in housing between then and now. This could also be used to explain the factors involved in the spread of the epidemic. A flaw in this approach would be that many of the structures from that period are probably gone. In this case, a 3D model could be built to represent neighbourhoods or buildings that have disappeared. Any of these projects could be useful in depicting the period in greater, more immersive detail, in order to help visitors better understand how people lived during the outbreak of epidemics.