John Snow’s well known cholera map is often cited as one of the earliest known examples of using geographic inquiry to understand a health epidemic. Starting on August 31, 1854, an outbreak of cholera hit the London district called Soho. Over the course of three days, 127 people died from the disease and by September 10, over 500 had died. Physician John Snow was able through talking to local residents and his geographic analysis of cholera deaths, narrow down his suspicion of the source of the disease to a water pump on Broad Street. Snow mapped out the locations of the local water wells and cholera deaths to back his argument about the contaminated pump, convincing the local council to remove the handle to prevent its use.
This early use of mapping in epidemiology is a popular example used in many GIS textbooks and courses to highlight the application of geographic analysis.
Those that want to explore the cholera data in GIS format can do so thanks to Robin Wilson of Southampton University. Wilson georeferenced a scan of the original Snow map to the Ordnance Survey National Grid from which he then digitized the plotted locations of cholera deaths and pumps. Wilson has made all of the GIS data freely available for downloading in a ZIP file. The file includes the georeferenced scan of John Snow’s map, shapefiles of the cholera death locations and pumps, and several color and grayscale OS map images. Users can use GIS software such as ArcGIS or QGIS to load the geographic data and georeferenced maps to created their own John Snow cholera maps.
Simon Rogers over at the Guardian’s Data Blog has taken the data prepared by Robin Wilson and used CartoDB to create an interactive map. Rogers opted for the Stamen ‘toner’ as the base map to mimic the original look of Snow’s map. At the bottom of the article, Rogers has made the data available in Google Fusion Tables for those that want to explore Snow’s cholera data further. From there you can create your own map using Google Maps or export the data in KML format.