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Map Datums and Location Formats
Map Datums are based on a mathematical model of the Earth.
What Are a Map Datums?
A datum is a mathematical model of the Earth that 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 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 you
can set the GPSMAP 378/478 to match most of those commonly
used.
If you are navigating and comparing the GPS coordinates to a map,
chart, or other reference, set the map datum in the GPS unit to the
same datum as the map to ensure the most accurate navigation.
What is a Location Format?
Your current location can be viewed on the GPS in the form of
coordinates. Because 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 used by all
Garmin units.
You can choose to change the location format to use with other
coordinate systems in the Location eld of the Setup tab—Location
sub tab. UTM/UPS (Universal Transverse Mercator/Universal Polar
Stereographic) are easy-to-use metric grids that are found on most
USGS topographic quadrangle maps. You can also select one of
several other grids, including a user-denable grid (for the advanced
user).
For more information about using paper maps with your
Garmin unit, refer to Using a Garmin GPS with Paper Land
Maps, available for download at www.garmin.com/manuals/
UsingaGarminGPSwithPaperLandMaps_Manual.pdf.
126 GPSMAP 378/478 Owner’s Manual
APPendIX > MAP dAtuMs And locAtIon forMAts