William Farr, 'Diagram Representing the Mortality from Cholera in Different Elevations 1848–49' from Report on the Mortality of Cholera in England, 1840–50. Wellcome Library, London.
Farr's Report offers some exceptional visual explanations of cholera mortality data. Contrary to Snow, Farr's analysis was leading him to the conclusion that elevation above sea level was the key factor in the communication of cholera. Whilst his diagram clearly hows the relationship between lower ground elevation and higher mortality, this association was due to differences in water sources in these locations. It is a reminder of how visualisations containing false associations have the power to mislead us.