The program makes a map using John Snow's 1854 Cholera data.

Hints:

After making a backup copy of the disk,

copy the

      CHOLERA.EXE, PUMPS, STREETS, DEATHS, TESNEDGE.DAT

files to a RAM disk and then type

      cholera

The program will then draw a street map, display the location of the deaths,
followed by the location of the wells. You can also run the program from a
disk, by just typing cholera, but this is a little slower. The program and 
the data files must all be in the same directory. When you've seen the map 
press "enter" again, and again, ....

The data consists of the relevant 1854 London streets, the location of 578 
deaths from cholera, and the position of 13 water pumps (wells). 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 significance of the map is that, by closing the Broad Street pump by
removing its handle, Dr. Snow stopped the epidemic, and 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

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. Scale of the source map is approx. 1:2000
Coordinate units are meters. 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. 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.

Waldo Tobler
National Center for Geographic Information and Analysis
Geography Department
University of California
Santa Barbara CA 93106-4060

tobler@geog.ucsb.edu
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