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Set of numbers that describes your location on (or above) the earth. These may be either latitude (N or S) and longitude (E or W), which is the Universal Transverse Mercator system, or UTM coordinates, which measures distance in meters from the equator (N or S) and a prime meridian (E or W). UTM is based on a grid-system that divides the Earth into 6 deg. longitudinal slices, 100,000 meters high. Another system, MGRS (Military Grid Reference System), is based on UTM, but divides the UTM sections into even smaller subsections. It will primarily be found on military GPS receivers only.
2-D and 3-D Coordinates:
Your horizontal location, such as latitude and longitude, is called a 2-D coordinate. It is available, by default, on some GPS receivers, and requires a minimum of 3 satellites to get a 2-D location. Sometimes, if satellites are obscured by trees, mountains, or buildings, you may only get a 2-D location.
When you get latitude, longitude, AND altitude, that is called a 3-D coordinate, and requires a minimum of 4 satellites visible. Almost all GPS receivers provide this as a standard.
When your receiver obtains information from GPS satellites to determine what coordinates you are at, it provides you with a position fix. Each receiver has a minimum number of satellites it must be able to "see" (usually 4 satellites minimum for "3-D" coordinates), to give a good position fix. Most GPS units allow you the option of marking and storing your current position as a landmark or waypoint. Some even allow you to name your position (CAR or DOCK) or attach an icon.
Landmark or Waypoint:
This is a position that is stored into the GPS unit memory. Your position is not a WAYPOINT until you SAVE IT. It may be from a position fix that you have taken, or you may input the coordinates of other locations that may be intermediate or final destinations. The GPS unit will either give the position a name, such as LMK02 or LOC 01, or you may provide a name that you will easily recognize, like CAMP. (NOTE: when you start your journey, it is usually wise to store your starting position, especially if you are planning to return!).
Newer mapping units allow you to look up addresses, cities, points of interest and other places in the mapping database that is built-in or that you may have downloaded from a CD. You can save these as a waypoint that you can easily refer to later. You can enter several addresses of clients before you leave home, and then easily "find" them later.
There are software programs available from the GPS manufacturers and from outside vendors, that let you mark waypoints directly on a map on your PC, and then load them into your GPS. Conversely, they usually also let you download waypoints you have saved in your GPS to the program, and then let you save them as a data file on your computer.
A route contains a starting and an ending position, as well as intermediate locations along the way. Each segment between positions is called a leg. Routes can be made up of one leg, or a series of legs. If you are going on a hike, you might input a route composed of the trailhead, planned rest stops or camp sites, and your destination. Some units allow you to backtrack, or reverse your route.
There are two basic ways to use a route:
(1) If you are planning a hike, or trip, you can extract the coordinates of your waypoints from a highway map, topographic map, or map software. This is extremely helpful, whether you are planning a Scouting adventure, or visiting a business client or long-lost relative. Some GPS receivers let you plan your trip on a computer, and upload the route into the receiver.
(2) If you've taken your GPS receiver on a hike or off-roading, etc., and you recorded your waypoints as you traveled, you can come home and copy or download your trip, and find out positions of that prize-winning vista, the best fishing spot, that rare bird you saw, or the cave you got trapped in during bad weather. If a member of your party is injured, a volunteer can hike out and provide exact coordinates of that location to rescuers. Search and Rescue personnel can download completed search routes to record where all the teams have been.
Track, or BackTrack
When you walk or drive with your GPS on, most handheld receivers will record the path you take as a dotted line, referred to as a "bread-crumb" trail or "track". This lets you see where you have been. Most receivers have an option that lets you save the track to memory, and they will let you select the track as a "backtrack" or route option. This way, if you get lost, or just want to go back the way that you came, the GPS will direct you where to go. When the GPS saves a track, it usually consolidates the track to a fixed number of waypoints (ie 300), so it will not duplicate the path exactly.
GPS receivers let track files save a limited number of track points (1000-3000), and then usually over-write the initial points when you reach the maximum, so that the beginning of the journey disappears. Receivers record track points at a default interval ("X" miles or "X" minutes), but many let you change the interval, if you want to make the track last longer.
Advice: If you are starting a journey or a hike, it is wise to save or reset/empty the track file, so that if you need to backtrack this journey, it is not contaminated by previous trips.
GPS units can provide elevation information (altitude, usually above sea level) if a minimum number of satellites are visible (at least four). Due to the nature of GPS, this will be less accurate than your horizontal position (See GPS Receiver Performance, below)
This is the direction that the GPS receiver is moving over the earth's surface, not necessarily the direction the unit is pointing. This is best viewed while moving, because the value stops if you do. Heading is a value in degrees in a clockwise direction, between 0 and 359 and it corresponds to compass values.
If you pick a landmark or waypoint, and you want to know which direction it is from where you are now, you need to know its bearing. This is a direction in degrees, in a clockwise direction from north. It is the direction you need to head in order to reach the selected point. If the bearing to your destination is, for example, "270 deg." and you are on heading "240 deg", you are traveling 30 degrees away from your target. Now this may be OK if it is the way the trail goes, but if it goes to far off, you may be on the wrong path--Check your map!