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80 GPSMAP 76Cx Owner’s Manual
APPENDIX > MAP DATUMS AND LOCATION FORMATS
Map Datums and Location
Formats
What Are 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
specific map datum. Every chart has a map datum
reference and the GPSMAP 76Cx 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, set the
map datum in the GPS unit to the same datum as the
map to insure 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. 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-
definable grid (for the advanced user).