Garmin eTrex Vista Cx Owner's Manual - Page 104

APPENDIX > MAP DATUMS AND LOCATION FORMATS Map Datums and Location Formats Map Datums are based on a mathematical model of the Earth. 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 94 reference and the Vista Cx 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 ensure the most accurate navigation. What Is a Location Format? Your current location is 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 for other coordinate systems. UTM/UPS (Universal Transverse Mercator/Universal Polar Stereographic) projection formats 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 userdefinable grid (for the advanced user). eTrex Vista Cx Owner's Manual