Density Equalizing Map Projections (DEMP)
The technique of using cartograms, or Density Equalizing Map Projections (DEMP),
for analyzing geographic distributions of disease, was pioneered at Lawrence
Berkeley National Laboratory (LBNL) beginning in 1985.
The latest algorithm is the result of ten years of development at LBNL.
The DEMP concept is deceptively simple and has been implemented with at
least a dozen different algorithms, including three of our own.
However, solving moderately sized problems (500 polygons)
in a short time (20 minutes) on affordable computers ($5000) has proved to be
much more difficult than we originally anticipated.
The DEMP technique is appropriate, and even works at its best,
when the number of cases
is too small for the calculation of stable rates. It is ideally suited for
investigating small-area health effects related to factors such as
socioeconomic status, cancer screening programs, and environmental hazards.
One-page example
(breast cancer in San Francisco Bay Area)
LBNL DEMP bibliography
DEMP software (RLint)
other DEMP-related software
DEMP processing of user map files
appropriate use of density equalized maps
some pitfalls in the use of DEMP maps
index.html 6/29/96
dwmerrill@lbl.gov
http://merrill.olm.net/dwmerrill.html