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96/96C Owner’s Manual 125
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What are Map Datums?
A datum is a mathematical model of the Earth which
approximates the shape of the Earth and enables
calculations to be carried out in a consistent and
accurate manner. The datum is physically represented
by a framework of ground monuments (i.e. trig.
stations) whose positions have been accurately
measured and calculated on this reference surface.
Lines of latitude and longitude on a map or chart are
referenced to a specic map datum. Every chart has
a map datum reference and the GPSMAP 96/96C can
be set to match most of those commonly used.
If you are navigating and comparing the GPS
coordinates to a map, chart or other reference, the
map datum in the GPS unit should be set to the same
datum as the map or chart to ensure the most accurate
navigation.
What is Position Format?
Your current location can be viewed on the GPS in
the form of coordinates. Since different maps and
charts use different location formats, Garmin GPS
units allow you to choose the correct coordinate
system for the type of map you are using. The most
common format is latitude and longitude, which is
utilized by all Garmin units. On most models, you can
choose to change the position format to use with other
coordinate systems. UTM/UPS (Universal Transverse
Mercator/Universal Polar Stereographic) are easy-
to-use metric grids that are found on most USGS
topographic quadrangle maps. Several other grids,
including a user-denable grid (for the advanced
user), can also be selected.