So what's this GPS all about then? It’s a system that lets you know exactly where you are in the world explains Darren Lock. Location, location GPS (Global Positioning System) is a revolution in navigation that uses space-age technology to pin-point a specific location, either on the ground, at sea or in the air. 20,000km above our heads, the Navstar Global Positioning System uses 27 satellites to triangulate the position of a GPS receiver. Each satellite knows where it is in relation to the Earth and the other satellites by regularly communicating with base stations back on Earth. By measuring the distance between a device and at least four satellites, it's mathematically possible to pinpoint and confirm your exact position. This mathematical principle is called triangulation – the fourth satellite is used to ensure the other satellites are all telling the truth. Currently, consumer GPS can pinpoint your location down to the nearest 15m or so. Let's take a look at the different kinds of devices on offer. Handheld GPS There are a number of handheld GPS units on the market and they can be broadly divided into two types: those that can be used in conjunction with maps and those that can't. GPS handsets without the mapping function can be considered as entry-level devices as they offer the most basic features. The Garmin eTrex (around £80) is one of the cheapest units available and if you enter a target's co-ordinates it will estimate the distance to that target. Of course, there's no map to use, so with GPS receivers of this type, your route is only as good as the target co-ordinates you provide. If you want to raise the stakes and have a more visual indication of your route, then it is worth investing the extra cash on a mapping GPS receiver. One of the best value mapping GPS units is the Magellan eXplorist 200 (around £130), which has a built-in background map of Europe and features a bright, backlit screen. The unit can store up to 20 routes or 500 waypoints and is built like a tank. GPS in your car One of the growth areas in GPS systems is motoring. In fact, if you have a navigation device in your car then you already have access to GPS technology, possibly without even realising it. One of the most popular in-car navigation system brands is TomTom. The TomTom units started out as an add-on to PDAs, but now the company is producing standalone in-car units. The top-of-the-range TomTom unit is the GO 300 (around £380), which features a large colour LCD screen and provides a variety of 3D navigation views. Plotting your course is easy: just type in the postcode of your target location and a route is plotted for you. The unit works without any extraneous PC interaction too, so you can simply plug and play. Many other manufacturers such as Garmin and Magellan also produce devices of this type. If you already have a PDA and fancy saving yourself a bit of cash on an in-car navigation system, you can buy add-ons that will give your handheld PC this functionality. Check out the TomTom Navigator 5 (around £200), which gives you all the features of the GO 300, but at a fraction of the price. Continued on page 2..

13th July 2007