Garmin aera 660 Pilot’s Guide
190-02017-20 Rev. E
Appendix I
211
Overview Navigation Flight Planning Hazard Avoidance Additional Features Appendices Index
APPENDIX I: MAP DATUM AND LOCATION
FORMATS
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 (such as
trig. stations) whose locations have been accurately measured and calculated on
this reference surface. Lines of latitude and longitude on a chart are referenced to a
specific map datum. Every chart has a map datum reference and the aera 660 can be
set to match most of those commonly used.
LOCATION FORMATS
Your current location can be viewed on the GPS in the form of coordinates. Since
different charts use different location formats, Garmin GPS units allow you to choose
the correct coordinate system for the type of chart you are using. The most common
format is latitude and longitude, which is used by all Garmin units. You can change the
location format to use with other coordinate systems. Several other grids, including a
user-definable grid (for the advanced user), are available.
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