Data science foundations: John Snow's Cholera map

1854 Soho Cholera Outbreak

In 1854, Soho was paralysed by the 'Blue Death.' At the time Cholera was seen as a cursed infection which could kill a healthy person in twelve hours. As the area succumbed to an epidemic which led to 600 deaths in just 10 days, Dr. John Snow ignored the 'poison air' theories and hunted the source through the streets. He created his iconic map as forensic evidence to prove the link to the Broad Street pump (pictured yellow), finally birthing modern epidemiology.

Density: The Heatmap

Beyond simple points, visualisation techniques for identifying clusters have evolved. Modern heatmaps visualise incident density. This spectrum reveals the outbreak's intensity and mathematical epicenter, reinforcing the visual evidence of the cluster.

Structure: The Hex Map

Furthemore, Hex maps aggregate data into geometric bins. Adjust the resolution below to see how the cluster structure changes as we change the size of the hexagon and boundary size.

Teaching the Computer

How do we teach computers to detect patterns as we do as humans? K-Means clustering is one way of mathematically identifying the central 'heart' of an outbreak by iteratively averaging the distance between all individual casualties (click play).

Data drives decision making

The algorithm converges where the data dictates—right near the Broad Street pump. Every life lost provided the mathematical gravity that pulled our model to a convergent truth.

The Legacy of John Snow

Dr. Snow's mapping laid the foundation for spatial analysis. Today, these tools help global experts track and predict the spread of infectious diseases.

Data Source Repository