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Appendix
Map Datums and Location
Formats
Location Formats
Map Datums
Map Datums are based on a mathematical model of the Earth.
What are Map Datums and which should I use?
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 spe-
cific map datum. Every chart has a map datum reference and the iQue
handheld 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 insure the most accurate
navigation.
What is a Location Format and which should I use?
Your current location can be viewed on the GPS in the form of coor-
dinates. 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. You may choose to
change the location format to use with other coordinate systems in Loca-
tion Preferences. 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-definable grid (for the advanced user), may also be selected.
