Workshop Content
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Workshop activity
Activity - Dr. John Snow’s Cholera Map (1854)
Dr. John Snow theorized that the cholera outbreak was attributed to contaminated water. He mapped the location of the 13 water pumps in the Soho district of London, and the location of those who fell ill, and noticed a concentration around one particular pump on Broad (now Broadwick) Street.
This exercise will be an introduction to the QGIS interface, in the replication of Dr. Snow’s map.
Data sources:
- Point data, courtesy of Don Boyes (University of Toronto), for water pump and cholera case locations (file size: ~26 KB)
- OpenStreetMap data for the Greater London area (file size: ~77 MB)
Part 1 - Create a basic map
Part 2 - Basic spatial analysis
Using Snow’s theory that the source is contaminated water from the pumps, we’re going to determine which pump serves the greatest number of people affected, based on their proximity to the pump.
Thiessen polygons are drawn in such a way that the boundaries represent the halfway point between neighbouring pumps. Therefore, any location within a polygon is closer to the pump within the same polygon, than any other pump. These polygons will be used to calculate the concentration of cases per pump.
Reference material
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