GPS stands for Global Positioning System is a system whereby satellites orbit the Earth broadcasting signals to the relevant receivers. These receivers can then process this information and determine where they are. The GPS system was originally created by the US military but is completely free to use. You may have used it on your mobile phone or sat-nav system in your car.

So why is GPS useful for walkers? Well, it helps determine where you are on the ground - to an accuracy of around 10m. This helps walkers stay on the right track and stops them getting lost.

The location given by your GPS can then easily be converted into an Ordnance Survey (OS) map allowing you to find new locations, possible dangers or simply go back the way you came.

What features do you need?

GPS systems all essentially do the same job - they tell you where you are and where you've been. Other features are available, but if you're unsure, simply go for an entry level system such as the Garmin eTrex .

Features to consider include:

• readability of the screen
• ease of use
  
• battery life - very important
• durability - is it hard-wearing enough to survive years worth of being thrown in bags etc? Or does it simply look nice but will fall apart?
• memory - make sure it has room for at least 20 routes and 500 waypoints.
  
• PC connectivity (for advanced functions) 
• water-proof - are you going out in the rain? Then this is a must.
• back-light - can the system be used at night?

Choosing your GPS

There are other factors to consider too, but these are for you to make your own mind up. Make sure you don't spend too much if you're only an occasional walker - the most basic system will probably do the job.