aeronautical charts. Because the angular relationships shown on the map are the
same as those on the globe, a navigator may draw a bearing, or a line of move-
ment, between two locations to plot a course. Even a tiny amount of distortion in
a conformal projection could result in a journey ending hundreds of miles off
course, if the distance to be traveled is great. Technological advancements like
GPSsystems have made navigation much easier in recent years, but selecting
the proper projection remains an important part of a navigator’s skills.Medical Geography
Medical geography is the study of the spatial aspects of disease and human health.
Like almost all phenomena associated with human activity, the incidence of dis-
ease exhibits a spatial pattern. By analyzing such patterns, a causal relationship
between disease and behavior, or disease and environmental factors, may be dis-
cerned. Such recognition may then be used in combating the spread of the malady,
and limiting the infection rate if the disease is contagious, or lowering the inci-
dence of the sickness if the environment or human behavior is responsible for
the disease. The individual often credited with founding this subdiscipline of the
field is Dr. John Snow, an English physician who treated patients suffering from
cholera during a severe outbreak in London in 1854. Snow acquired data on known
victims of the epidemic and used these figures to plot the number of deaths from
the disease onmapsof the city. He thereby determined that many of the victims
lived quite close to a water pump used as a water source, located on a busy
thoroughfare called Broad Street. At the time, little was known about how cholera
was transferred from person to person, and Snow theorized that the source of the
infection was the communal water pump. He called for authorities to shut it down,
and once it was closed, the number of deaths and rate of contagion dropped
abruptly. Snow had stopped a serious killer in its tracks by applying geographical
techniques to the study of disease.
In the era ofglobalization, diseases may spread quite rapidly following
international transportation routes, and modern medical geographers focus their
efforts on tracking the spatial distribution of diseases, determining their source
regions, and formulating strategies to block and contain new outbreaks. The prime
example of such research is the tracking and monitoring of the global AIDS epi-
demic. By using the techniques of medical geography, investigators have been
able to geographically pinpoint the source region of the HIV virus as lying in East
Africa, providing valuable clues to when and how the virus first entered the human
population. It is now believed that the HIV virus crossed over from primates,222 Medical Geography