| Term | Description |
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| Barometer | Air Pressure Sensor - Barometric altimeters use air pressure to determine your altitude. So when the weather changes, so does your elevation.
Satellite elevation can therefore often be more accurate than one derrived from pressure and is typically within 100 feet w/o need for calibration Some units allow you to use the GPS to set the barometer. Any GPS can determine your elevation without having a barometer while you are receiving 4 or more satellites. Vertical accuracy is typically twice the estimated position error,
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| Contour Lines | Lines on a map having the same elevation - The closer the lines are together, the steeper the slope.
- To provide most useful information, they should not be more than 50 elevation feet apart.
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Electronic Compass | Electronic direction sensor Any GPS can show your speed and direction as long as you are moving with reception. Electronic compass accuracy is typically +/- 5 degrees or worse Work best when horizontal, some can be used when tilted (2 or 3 axis compasses) Usually must be recalibrated each time you change batteries. GPS only requires speed of a few miles an hour to determine direction. As speed increases, the accuracy of speed/direction is improved. |
| Elevation | Distance above Sea Level - AKA altititude GPS vertical accuracy is typically twice the estimated position error, Barometric altimeters usually reflect minor/short term elevation changes better than GPS altimeters. |
| EPE | Estimated Position Error
An estimate of the accuracy of your position. This is only and estimate and is calculated differently between vendors/units. "Rule of thumb" for elevation accuracy is twice the horizontal accuracy. Accuracy is determined by how well the satellites used are spread.
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| Geocaching | Geocaching is a new twist on an old sport - See GPSmagazine full description An outdoor GPS game where you search for "treasure caches". You can log your visit and exchange "trinkets". |
| GPS | Global Positioning System
A system of 24 active satellites that orbit the earth sending signals that allow a receiver to triangulate it's location. (There are always a few "spares" aloft.) Signals from 3 satellites are required to determine your position. Signals from 4 allow you to know your elevation as well. The accuracy depends on how well the satellites are spread apart. |
| GPSr | GPS Receiver User portion of the Global Positioning System |
| GPSs | GPS Satellite - AKA bird Satellite portion of the Global Positioning System |
| GPS Scale | Relationship of distance on GPS screen to real world distance. A graphic scale showing how the width of scale bar on screen relates to real world distance. On Lowrance, the distance is for the width of the screen. |
| Icon | Generically means a symbol Graphical representation of waypoint on GPS screen. On Lowrance units, a symbol for unnamed icons that can't be navigated to.
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Latitude Longitude | Coordinates of a position - See Map Coordinate System |
| Magnetic Declination | Difference between "Magnetic North" & "True North" Caused by the magnetic & geographic poles not being in the same place. Varies by location Specified in degrees E or W (10 degrees E at Denver) The difference changes over time
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| Map Clutter | Having too much data displayed on a screen makes it hard to see what you need. |
Map Coordinate System | Model to specify locations on earth surface. - Latitude Longitude height reference is most common
- References are the Equator & Prime Meridian
- Coordinates can be prefixed N|S & E|W
- Areas to west of Prime Meridian or below equator are negative numbers
- Can be described via different position formats: (Confluence Park)
- Degrees (N 39 45.287 W 105 0.551)
- Degrees, Minutes (N 39 45.287 W 105 0.551)
- Degrees, Minutes, Seconds (N 39 45' 17.2" W 105 0' 33.1")
- UTM - Universal Transverse Mercator
- Allows for easier distance calculations between coordinates (metric based)
- Comprised of zones:
- Zone numbers designate 6 degree longitudinal strips
- Zone characters designate 8 degree zones N & S from Equator
- There a special zones for above 84 degrees N and below 80 degrees
- Measurements are refered to "Eastings & Northings
- Confluence Park: (13 S 0499213 4400541)
- Zone 13 S
- Easting 0449213
- Northing 4400541
- MGRS - Military Grid Reference System is an extension of UTM
- GPS units will do transformations between systems they support
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| Map Datum | Model used to approximate shape of earth. - There are hundreds of datums used around the world.
- WGS 84 is the most common Datum used by GPS systems in the US.
- Differences using US datums should be < 100 yards in error (usually much less).
- GPS units will do transformations for Datums they support
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| Map Orientation | GPS display setting that controls how you view the map Usage varies by unit. - North up - North always is at the top of the display
- Track up - Direction you are currently heading is at top of display
- Course up - Direction of next navigation point is at top (reverts to track up when not navigating)
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| Map Scale | Relationship of distance on "paper" map to real world distance. E.g. on a "24K" map, one inch on map is 24,000 inches on earth. Scale also usually provided graphically on map legend or GPS screen.
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Map (Raster) | A map made from scanning a paper map. (Composed of a bunch of "dots") Typical examples are USGS Quad maps, satellite or aerial imagery. |
Map (Vector) | A strictly digital map that displays objects. (lines & points & shapes) This type of map is visible at all zoom levels. Requires small amounts of memory. GPS can often control screen "clutter" automatically. Usually will not follow roads, trails, streams as closely as a vector map.
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| POI | Point Of Interest Usage varies by unit. - User POIs are also known as waypoints
- System POIs may show cities, businesses, or other places of interest.
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Proximity Waypoints | Waypoints that you will be notified about when you get within a specified distance or time. Useful for avoiding hazards. (e.g. Underwater rocks, reefs, speed zones) |
| Route | A series of points that a GPS can use to guide you to in order automatically. As you approach each turn point the GPS may notify you When turn is reached, the unit then guides you to the next point. Routes can be reversed to quide you way back.
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| Routing | Ability of a GPS to automatically generate a route given a destination. (AKA - turn-by-turn) Outdoor units provide on screen indication of approaching turns. Garmins automatically recalculate after a missed turn and also provide route previews. |
| Sensors | Garmin term for electronic compass & barometer/barometric altimeter |
| Tracklog | A series of points that a GPS can automatically create as you travel. Also known as a "bread crumb trail". Most GPS units allow you to navigate these after you save them, as you would a manually created route.
(The unit creates a route from the saved tracklog data and may require an available track slot) |
| UTM | Universe Transverse Mercator - See Map Coordinate System |
| WAAS | Wide Area Augmentation System
A system designed to improve the accuracy of GPS. Uses GeoSynchronous satellitesthat that send information to your GPS to correct for atmospheric or other anomilies. (AKA EGNOS in Europe)
The US system has a satellite over the Atlantic equator & one over the Pacific. These satellites are much higher in altitude than the others, but are still low in the sky for Colorado. This means reception accuracy improvement here is often problematic. |
| Waypoint | A point that you manually set. Waypoints can be searched for and navigated to at a later time.
On some receivers they are referred to as POIs (Points Of Interest). |
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