GIS Analyses of Dr. Snow’s Map Snow’s map, demonstrating the cholera deaths clustered around the Broad Street well, provided strong evidence in support of his theory that cholera was a water-borne disease. Snow drew Thiessen polygons around the wells, defining straight-line least-distance service areas for each. Each Thiessen polygons is comprised of boundary segments that perpendicularly bisect line segments drawn between the point it contains and adjacent points. A large majority of the cholera deaths fell within the Thiessen polygon surrounding the Broad Street pump, amd a large portion of the remaining deaths were on the Broad Street side of the polygon surrouding the bad-tasting Carnaby Street well.

GIS Analyses of Dr. Snow’s Map

Snow’s map, demonstrating the cholera deaths clustered around the Broad Street well, provided strong evidence in support of his theory that cholera was a water-borne disease. Snow drew Thiessen polygons around the wells, defining straight-line least-distance service areas for each. Each Thiessen polygons is comprised of boundary segments that perpendicularly bisect line segments drawn between the point it contains and adjacent points. A large majority of the cholera deaths fell within the Thiessen polygon surrounding the Broad Street pump, amd a large portion of the remaining deaths were on the Broad Street side of the polygon surrouding the bad-tasting Carnaby Street well.