Question 3: What is the value of combining geographic information?
A
single set of geographic information is limited in its analysis potential.
It can be used to provide information about the location of the features to
which it relates, and this can be used as the basis for recording and investigating
distributions. However, it cannot be used to investigate interactions with
other sets of geographic information. This ability to investigate the ways
in which two or more sets of geographic information interact with one another
is the ultimate goal in much of the work undertaken in geographic information
systems.
Combining geographic information themes is a lot more powerful. The geography,
or location, is used as the common denominator – the link. It has the
potential to generate new information on patterns and relationships between
multiple sets of geographic information that would otherwise be missed, and
to aid in answering more complex questions or decision-making. Why do patterns
exist and what impact might they have?
The classic demonstration of this is Jon Snow’s investigation of Cholera
in Victorian London in 1854. Jon Snow plotted the locations of incidences of
Cholera against the location of water pumps, and noticed how they clustered
around the Broad Street water pump. He identified the contaminated source
and created the beginning of modern epidemiology. A map of just the water
pumps or incidences of Cholera alone would have been of little value.
Cholera incidences represented as lines around the Broad Street pump.
Map in Snow’s 1855 book (http://www.ph.ucla.edu/epi/snow.html)
Another example is flood risk maps. This combines geographic information
relating to the locations of properties and the locations of flood zones
to identify properties at risk of flooding. Studied separately, these
two themes of geographic information tell us very little. By combining
them, we create new information. This combined information is of huge
value to environmental groups and insurance companies.
Essentially, combining geographic information adds value to an analysis by
providing new information that would not be detectable otherwise.