Geography Reference
In-Depth Information
and weather it provides accurate positional information. Some map makers
have started to change their map designs to make it easier for hikers to use.
Some tourist areas offer GPS for people to help them follow a certain tour.
Aids for the Visually Impaired. Combined with acoustic or tactile signal-
ing devices, GPS can be used to help visually impaired people find their way
in new settings and navigate places that rapidly change—for example, a state
fair or a college campus, as was done by Professor Reg Golledge and others
at the University of California at Santa Barbara.
The U.S. GPS system is widely and freely available, but because the U.S.
Department of Defense controls it, people in other countries have little or no
inf luence over its operation or when it might be shut down. The
Commonwealth of Independent States (CIS) has a satellite system, which
operates similarly to the U.S. GPS. But it has fewer satellites, offers less cov-
erage, and is only available to people with very expensive receivers.
The European Union is currently developing a system, fully comparable
to GPS, called “Galileo.” Two prototype satellites were launched in late 2005
for testing. The full system, with 30 satellites and offering better coverage of
polar regions, will be operational some years later.
When maps exist, it is possible to convert them to GI using either tablet
digitization, heads-up digitization, or a scanner. The reasons for digitizing
from maps cover a gamut: the maps may be old and show something that
people want to compare to recently collected GI, the maps may be unusual
or hand-made, or the maps may be the only way of getting the desired GI.
Tablet digitizing involves the affixing of the source material (maps,
drawings, etc.) which are georeferenced to coordinates on a table digitizer, a
board of variable size. The location of the digitizer puck, the mechanical
pointer calibrated to the digitizer and freely moveable, is recorded as differ-
ent buttons are pressed. Software translates the location and button values.
Heads-up digitizing is similar, but requires that digitized source material be
georeferenced to a coordinate system. The material is displayed on a screen
and the person doing the digitizing uses a mouse or similar pointer device
and presses buttons to record locations. The scanning of existing map mate-
rial is also common, and because it is mostly automated is very fast com-
pared to tablet digitizing, especially when a large number of maps are to be
scanned. But scanning usually requires complex postscanning cleanup.
Hand digitizing is generally cheaper, but generally less accurate. Scanning is
expensive for just a few maps, and may be complex to configure, but it gets
cheaper if you have a number of maps prepared in the same way.
Keep in mind the following advice when preparing or working with sur-
veyed, GPS'd, or digitized data:
Search WWH ::

Custom Search