Tooling up for Complexity - Participatory Mapping: New Data, New Cartography - page 16

the itineraries of epidemics. This theory puts forward the
existence of an “infecting agent” intrinsic to the diseases and
which explains the epidemics. Due to a shortage of evidence,
the adherents of this theory mistook the effects of the
epidemic (such as its dispersion in different places) for its
causes, so their maps showed the areas covered by an
epidemic [PAL 96, p.89]. On the contrary, the proponents of
a modern medicine opted for distribution maps. By
visualizing both the geographical extent of the disease and
the number of victims, and by combining these data with
local data, physicians could then explain the source and
mode of propagation of the infection.
Medicine in the 19th Century was a field of
experimentation for the graphic semiology of maps, but also
to illustrate the overlap between the power of the gaze and
the processing of the population as statistical data. The map
made by John Snow during the cholera epidemics in London,
1854 is an example of the demonstrative power of
distribution maps. In order to prove his theory on the
propagation of cholera through water - and not through air
as preconized by the dominating theory at the time - John
Snow plotted the number of victims and the sources of water
in the neighborhood of Soho in London [JOH 07]. He did this
with the help of a map by combining the number of dead per
building with the water pumps used by the inhabitants, and
was able to show the responsibility of the latter, including in
Broad Street. Snow went to see the authorities with his
graphic evidence and requested that the water pump
responsible for the contamination be shut down immediately.
Snow used this map to show that mortality rates were
related to the water pumps, but also to reason by exclusion,
showing why other households had low mortality rates.
Snow compared, for instance, the situation of highly
impacted households around the water pump on Broad