The significance of Snow's famous cholera map 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.
The data in these files were digitized in 1992 by Rusty Dodson of the NCGIA, Santa Barbara, from the map included in the book by John Snow: "Snow on Cholera...", London, Oxford University Press, 1936. 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 are used by Dodson for a student exercise in NCGIA TR-93-5, "Teaching Introductory Geographical Data Analysis with GIS....", May 1993. Death coordinate order randomized and Thiessen polygon boundaries added by Waldo Tobler.
The program was written 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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