An Interactive Visualization of the
1854 London Cholera outbreak
mreda2 at uic dot edu
Note: Safari users, please use Up/Down arrow keys to zoom in/out of the map. Mouse wheel support in Safari is broken.
Source code (licensed under GPLv3): SnowCholera CholeraData CholeraDay ClusterGrid DeadPerson Grapher Slider TimeSeries TimelineWidget VectorMap Visualizer misc
In 1854, a cholera outbreak swept over the Soho district in London. The outbreak reached its peak on the first week with more than 150 deaths, causing wide spread panic in the neighborhood which lead to the flight of its residents. At that time, the cause of cholera was not scientifically established, and people believed that toxic vapors resulting from the decay of organic matters was the cause of cholera, among other diseases. Dr. John Snow (1813 - 1858) was skeptical of this theory. To investigate other causes, Snow made his famous map of the Soho district, plotting the location of deaths alongside street water pumps in the neighborhood. At that time, the data acquisition and visualization tools at Snow's disposal were severely limited by todays standards. Nevertheless, Snow's visualization was arguably the first clear evidence that linked cholera transmission to contaminated water supply.
This project is aims to create an interactive version of Dr. Snow's visualization. The data used here comes from Snow's original map. Additional data was randomly generated and added to the original data such as gender and age of victims to make the visualization slightly more interesting.
The visualization is divided into two parts. The left side shows a map of the Soho district in London, plotting the location of deaths, as well the location of street water pumps. The right side of the visualization shows 3 different graphs showing the total number of deaths per day, the percentage of male/female victims, and the percentage of various age groups. Underneath the graph is a timeline with two sliders allowing the user to select a time-window (this is discussed in more detail later). A clustering slider allows the user to turn on/off clustering and vary its coarseness (more in the later). The bar seperating the map from the graphs can be moved by dragging it to incraese the size of one side at the expense of the other.
The map occupies the left side of the visualization. It plots the location of deaths along with the location of street pumps. The user can zoom in/out of the map using the mousesheel (or using UP and DOWN arrow keys in Safari, which for some reason doesn't send mousesheel events to the Java applet). The map can also be panned by dragging with the left mouse button.
The icon for a victim is either a triangle for a male victim, or a circle for a female victim. A circle is significantly different in terms of visual features from a triangle. Thus, it should be easy for the analyst to distinguish between a male and a female victim, or to conduct a quick visual search based on gender. The male's triangles are isosceles, and are rotated about -40 degrees. This, based on my subjective judgement, made them a bit easier to notice. Pumps are depicted with white diamonds with a thicker outline, which should make them pop out as they're significantly different in shape and color from the victims.
The color of a victim's icon is used to represent the age of the victim. The color scale goes as follows:
|10 - 20|
|21 - 40|
|41 - 60|
|61 - 80|
The color progresses from dark blue to cyan to yellow to red. The cyan color blends a bit of green and blue, which makes the color distinct even for people with some form of color-vision impairment. Here's how the scale looks like for people with Deuteranopia (red weakness):