Snow's Cholera Map

The significance of Snow's famous cholera map (a piece of which is shown here) is that, by closing the Broad Street pump by removing its handle, Dr. Snow stopped a major cholera epidemic, and thus demonstrated that cholera is a water borne disease. This was not previously understood. The map is the most famous and classical example in the field of medical cartography. For more details an informative source is: A. Cliff & P. Haggett, 1988, Atlas of Disease Distributions, Blackwell, Oxford, ISBN 0-631-13149-3.

In 1992, as part of the development work for an NCGIA technical report, Rusty Dodson of NCGIA Santa Barbara, digitized details from Snow's map reproduced in: 

 The scale of the source map is approx. 1:2000.  Coordinate units are meters.  The data in these files consists of:

Each coordinate point in the file "deaths" specifies the address of a person who died from cholera. When many points are associated with a single street address, they are "stacked" in a line away from the street so that they are more easily visualized. This is how they are displayed on John Snow's original map. The dates of the deaths are not recorded. 

The data files were created for a student exercise included in NCGIA Technical Report 93-5:

Death coordinate order was randomized and Thiessen polygon boundaries added by Waldo Tobler.

A program to display this data (cholera.exe) was written by Waldo Tobler on a 486 class PC, with a VGA display. It may not work quite correctly on other systems, but can easily be modified. [Hint:  if you are using Windows 3 or Windows 95, start the program inside a DOS window.]  It is also possible to change the colors, or to use dots instead of lines for the street map, or to slow the (random) time interval between the display of the individual deaths, etc. See the source code in "cholera.bas".  In order to get printed copies of the map(s) it is necessary to use a graphics screen capture program.

The coordinate data are also suitable for analytical investigations; e.g., bivariate density estimation, etc

The program in this data set (cholera.exe) makes a map using John Snow's 1854 Cholera data.  It will draw a street map, display the location of the deaths, followed by the location of the wells. Run the program by just typing cholera. The program and the data files must all be in the same directory. When you've seen the map press "enter" again, and again, ....

Prof. Waldo Tobler
National Center for Geographic Information and Analysis 
Geography Department 
University of California Santa Barbara CA 93106-4060
email: tobler@geog.ucsb.ed


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