Garmin eTrex Vista C color map navigator Owner's Manual

Also see for eTrex Vista C: Software guide Owner's manual

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Garmin eTrex Vista C color map navigator Owner's Manual Manual pdf 99 page image

88eTrex Vista CWhat are Map Datums, and which should I use?A datum is a mathematical model of the Earth which approximatesthe shape of the Earth and enables calculations to be carried out in aconsistent and accurate manner. The datum is physically represented bya framework of ground monuments (i.e. trig. stations) whose positionshave been accurately measured and calculated on this reference surface.Lines of latitude and longitude on a map or chart are referenced to aspecific map datum. Every chart has a map datum reference and theeTrex Vista C 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, the map datum in the GPS unit should be setto the same datum as the map or chart to ensure the most accuratenavigation.What is a Position Format, and which should I use?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 correct coordinatesystem for the type of map you are using. The most common format islatitude and longitude, which is utilized by all Garmin units. On mostmodels, you may choose to change the position format to use with othercoordinate systems. UTM/UPS (Universal Transverse Mercator/UniversalPolar Stereographic) are easy-to-use metric grids that are found on mostUSGS topographic quadrangle maps. Several other grids, including auser-definable grid (for the advanced user), may also be selected.Map Datums are based on amathematical model of the Earth.PositionFormatsMap DatumsMap Datums and Position FormatsAppendix