Geoscience Reference
In-Depth Information
on where in the world you are drawing the box? Why or why not? Based
on the above discussion of the France and Germany situation, the estimates
do indeed vary in quality and input sources depending on where you are
investigating.
Under the population map with the 1990 through 2015 data, access the
“SEDAC Map Client” or go directly to the map on
http://sedac.ciesin.columbia.
variables of your own choosing to the population data. What three variables
do you believe most directly influence population change around the world,
and why? What three environmental and other variables do you believe are
most directly impacted by rapid population growth and sustained high popu-
lation density? Your answers may vary, but variables that contribute to rapid
population growth include a high birth rate, a low death rate or a death rate
that is lower than the birth rate, immigration that exceeds emigration, good
health indicators, lack of deaths by natural hazards, major diseases, and
political instability, and agriculture or imports that can support population
growth.
10.4.2 Network analysis: Offline and online
10.4.2.1 Offline
Most of us were amazed when MapQuest gave us turn-by-turn directions
back in the mid-1990s on the web. Nowadays, routing is not only ubiquitous
in consumer mapping applications but is also embedded in thousands of
organizations around the planet, from delivery services to tracking ships. It
has become so familiar and expected that the complex computations requir-
ing mathematics, geography, and GIS are usually overlooked. When we find a
“route” we are looking for a connected path. That path might be analyzed in a
number of ways. Is it unique? Is it the shortest path? Is there, in general, more
than one shortest path (geodesic) in the given underlying geometry? Routing
depends not only on the accuracy of the railroads, roads, shipping lanes,
airline flight paths, and other mapped data, but also has come to depend
on real-time information inputs, such as traffic, construction, and weather.
Routing is also linked to and depends upon connectivity. Connectivity is a
broad topic.
In a mapping context, consider a subway map in which the scale and track
curviness are disregarded. The pattern of stops in correct relation to each
other, along unrealistically straight track, suffices for most commuters.
Curved lines are transformed into straight lines in this example often seen in
large cities. What is dominant is connectivity. In that context, you will now
have the opportunity to use various routing services in hands-on activities in
the next section. These include determining the shortest route for emergency
vehicles and the effect of traffic and barriers on travel time, distance, and
route.
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