While all GPS units will keep track of your whereabouts and guide you to a chosen location, mapping GPS receivers display this information on road maps, marking your position in relation to highways, lakes, landmarks and cities. The unit shows your current position with a marker, and the road map scrolls underneath, showing your progress. This makes mapping GPS units most useful for drivers.
Non-mapping GPS receivers (or mapping GPS units with the map turned off) display your movements by laying down tracklogs and waypoints (position markers), then "connecting the dots" to show your path, allowing you to retrace your route, but there's no road-map underlay. For most hikers, a topographical map is more important than a roadmap, but there is very little backcountry software available; outdoor experts emphasize not to toss your topo map because you buy a GPS – rather, the GPS will help you locate yourself on your map much more easily.
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