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Global Positioning Systems (GPS) are a navigational tool which uses information from satellites to determine the receiver’s position on the ground. GPS receivers are widely used in outdoor activities. However, they have some limitations:
- they can be slow to collect enough data to get a position fix
- they do not work well in canyons or ravines, inside, or under very thick or wet vegetation
- they require some skill to use to full advantage
- like anything electronic, they can break, become wet, or run the batteries flat.
We believe that the most useful aspect of carrying a GPS is the ability to quickly confirm your location when you’re not sure where you are. It simply forms one more piece of information (albeit a usually reliable one) in the navigational picture.
Contrary to popular thought, a GPS unit is not a replacement for a map and compass. The statement “but you can just punch the co-ordinates into a GPS and off you go” is wrong. Unless it’s a really high-end model, the GPS contains no internal map data. You can’t therefore see the ground around you without a traditional map; it won’t let you take backbearings, and you’ve got no idea if you’re on the correct track or not. Additionally, most GPS units don’t have an internal compass; a GPS only knows which way north is if it’s moving. Therefore, a GPS is not a substitute for a map and compass, and the skills to use them.
We have found the base-model Garmin eTrex GPS unit to be fast, accurate, and reliable on numerous occasions. It has a simple interface and rugged construction. The large screen is easily read, and it can be connected to a PC for pre-trip co-ordinate entry. However, as with many GPS units, the cord and software are an extra expense. The buttons are mounted on the side and it can easily be used one-handed, but the data-entry system is a little awkward for entering large numbers of co-ordinates. If you’re planning to do a lot of that, the cable and software might be a good investment.
The Garmin Gecko 101 uses very similar software, but in a much smaller, lighter package. Some people we have spoken to prefer the eTrex because of its slightly larger size. We found that the screen was a little small. Also, the users fingers tend to obscure the screen when pushing buttons, which are positioned above the screen. The mid-range 201 and high-end 301 models are PC-compatible.
The Magellan Xplorist 101 has a rounded, bright orange case. Its main feature, as far as we could tell from a five-minute shop demo, was the little joystick/button arrangement which allows the user to pan around the map. The menu/options system seemed comprehensive. Any of these three units would be suitable for outdoor use.
Map Coordinates & Zones
GPS users need to be aware that there are a number of different datum systems in use; the datum to which your GPS is programmed must match that used by your map. Otherwise, your coordinates will be inaccurate. This is commonly either Australian Geocentric Datum 1966 (AGD66) or Geocentric Datum of Australia 1994 (GDA94) format. Ensure that your GPS is set to the correct datum (GDA94 or AGD66) before entering data.
Australia is also divided into a number of map zones; it is important, particularly when using a GPS, that you also specify the correct map zone for the area you are in. Click icon to view a map of these zones 
Over-reliance on electronic devices is a potential cause of problems for a party which does not have the equipment and skills to do without that device. An obvious example of this is a party which sets off with a map and GPS but no compass or spare batteries. You should never rely solely on electronic devices if the safety of your party could be compromised by the failure of the device to work properly.
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