Owner's Manual - West Marine

Map Datums and Location FormatsMap Datums are based on a mathematical model of the Earth.What are a Map Datum and which should I use?A datum is a mathematical model of the Earth that approximatesthe shape of the Earth and enables calculations to be carried out in aconsistent and accurate manner. The datum is physically representedby a framework of ground monuments whose positions have beenaccurately measured and calculated on this reference surface. Linesof latitude and longitude on a map or chart are referenced to aspecific map datum. Every chart has a map datum reference, and youcan set the 276C Plus 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 thesame datum as the map to ensure the most accurate navigation.APPENDIX > MAP DATUMS AND LOCATION FORMATSWhat is a Location Format and which should Iuse?Your current location can be viewed on the GPS in the form ofcoordinates. Since different maps and charts use different locationformats, Garmin GPS units allow you to choose the correctcoordinate system for the type of map you are using. The mostcommon format is latitude and longitude, which is utilized by allGarmin units.You may choose to change the location format to use with othercoordinate systems in Location field of the Location Setup tab.UTM/UPS (Universal Transverse Mercator/Universal PolarStereographic) are easy-to-use metric grids that are found on mostUSGS topographic quadrangle maps. You can also select one ofseveral other grids, including a user-definable grid (for the advanceduser).For more information about using paper maps with your Garminunit, refer to Using a Garmin GPS with Paper Land Maps, availablefor download at www.garmin.com/support/userManual.jsp.276C Plus Owner’s Manual 117190-00501-00_0A.indd 1171/13/2005 10:44:13 AM