How to buy a GPS

26 June 2008 16:32

Which GPS will best help you navigate across the hills? These are the things to think about.

Do you need one?
GPS stands for Global Positioning System. It is a system of 27 Earth-orbiting satellites, which provide enough data to pinpoint any location on the globe when read by a GPS receiver. So this device is very useful, especially if you’re navigating across large, featureless areas.

Power
External power capability is useful if you’re planning to use a GPS in a car. But on the hill you’ll have to rely on battery power, so look for long battery life.

Screen
If you can’t read the screen easily you won’t be able to read the GPS receiver. Higher-priced units generally have larger, clearer screens, but you will save money if you can tolerate a simple screen. Colour screens make reading map detail easier.

Map datums
Map datums describe the irregular shape of the Earth for a particular region and different maps have different map datums. So GPS users must reference their GPS receivers to their maps. In the UK the GPS receiver must be set to OSGB or GRB36. For most European countries you need to use European 1950.

Routes
It’s useful to store a few routes plus a few escape routes or variations into a GPS, so you don’t have to reload data all the time.

System
GPS receivers are available as dedicated hand-held receivers, Smartphones, personal digital assistants (PDAs) with conventional PC capability, and as portable navigation devices (PNDs) that can be used in a car or on the hill. Each system has an advantage, but the dedicated outdoor systems are generally more robust and also offer a longer battery life.

Channels
GPSs use a numbers of channels to track the satellites. A 12 or 16 channel parallel receiver is now the most common and is better than an 6 or 8 channel parallel receiver as it can find the satellites more easily, particularly in built-up areas or woods.

Waypoints
Waypoints are coordinates of a location. If you want to store lots of routes, you’ll need a large memory built into the GPS receiver to handle all the waypoints.

Compass
Many GPS receivers boast a compass but they are rarely magnetic –so they won’t tell you which direction to move until you start moving. A GPS receiver with a digital magnetic compass built in will point you in the right direction before you start moving.

Computer links
Waypoint upload/download capability using software such as Memory-Map, Anquet, Magellan Topo or Garmin Topo is a must for regular users, as keying in waypoints manually is very slow.

Mountain maps
Digital mapping can show contours on the screen of your GPS receiver. Receivers that do not display mountain maps generally show your location between roads, but they lack the contour and cliff detail. 

Co-ordinate systems
UK maps have a grid so you can identify a location using a grid reference. But the commonest coordinate systems in the world are LAT/LON and UTM. So if you are using a GPS receiver in the UK, you must set the coordinate system to one that matches the coordinate system on the maps you are using, which is usually referred to as OSGB, ord srvy GB, or British Grid.