Satellite navigation systems will stop you getting lost but they do not come cheap

The author, Douglas Adams, was a great fan of satellite navigation for getting around the United States, where he lived in the latter part of his life. Invited to a party in a Californian town, he delighted in its efficiency, and his own failings. "I didn't know the way to San José," he said happily.

A satellite navigation system got him there, and for a growing number of people it's just the trick for deciding how to make complicated journeys around cities you don't know (or even parts of London you don't know).

The clichés are true: it ends the struggle to read a map or atlas on the passenger seat or over the wheel (which you know is dangerous). It also ends disputes with anyone designated navigator. Even if the machine gets it wrong, you can all agree it's stupid, which brings a harmony to travel.

If you've never experienced these systems, you may wonder what the attraction is. Indeed, research by the AA suggested most people don't even keep a road-map in their car, because they're always travelling between destinations they're familiar with.

But everyone I have spoken to who has tried satnav likes it, even for driving between places one knows, and misses it in cars that lack it. As well as being able to navigate you to any address (or in the better ones, postcode too) they can direct you to "sites of interest", such as filling stations, pizza parlours, railway stations, hotels, hospitals, shopping centres and cinemas.

The trouble is that it's a hard sell, because satnav is expensive: it calls for two interlinked bits of technology: a GPS (global positioning system) receiver, and a computer that can access digitised maps of the your area (or even the country), either held on a CD-rom or in the computer's memory.

The systems come in three flavours: installed, "aftermarket" (fitted by a dealer) and DIY. In effect, the first two are equivalent, because you don't get much chance to update the information on the CD-rom. This is a problem, because 10 per cent of the road network alters every year, as does the status of filling stations, pizza parlours and so on.

With the DIY systems - software you can load on to a handheld computer - there is a much better chance of being able to download updates from the internet. The DIY version is also cheaper, if less elegant. If you have satnav installed, it'll bump up the cost of your vehicle by £1,000, regardless of marque or model. Ford says that in the UK it has sold a total of 288,743 cars so far this year in which 1,035 have had satnav fitted (the buyer's option).

That's a paltry (my word) 0.36 per cent. "It isn't a standard feature on any of our cars, because customers prefer to choose if they want it," Philip Hale, a spokesman for Ford, said. "On Mondeos, 2 per cent of those sold had it fitted. The main reason more don't want it is the cost."

Slightly more fleet cars have them, but only top-of-the-range models. The Toyota Lexus and Jaguar S-type come with satnav as standard. Most other working folk have to make do with an A to Z.

So how does it work? The GPS part detects data transmitted by an group of 24 satellites orbiting 12,000 miles above Earth (so they move relative to the ground). Each has an onboard atomic clock, and transmits a constant stream of time signals. Your GPS receiver picks them up and calculates how long it took the signal to reach it. Get three satellite signals, and you can triangulate to a single point on Earth. Get four, and you can add altitude too. Most GPS navigation will work best when they can "see" five or more.

GPS was developed in the 1970s for the American military, but made available for civilian use in the 1980s. It's not perfect: the signals work on line-of-sight, so tall buildings and tunnels defeat it; expect your satellite navigation system to act up around (or inside) them. The more precise you want the location, the more the GPS receiver's manufacturer has to pay to the US Department of Transport for access to the necessary codes. Most of those in cars are accurate to between five and 10 metres, enough for most navigation.

The computer gets the GPS location, compares it with the digitised road-maps, squirts them to a screen (or just voice output), and bingo, you are here. With fitted or dealer-installed systems, you can't do anything with the computer. The advantage of DIY systems, besides being cheaper, is that they generally use the capabilities of handheld computers, particularly the Microsoft- powered PocketPC, plus a receiver you can slip in your pocket (or the glove compartment). That's a bonus, for while PocketPC machines aren't cheap (typically costing £300 upwards) you can also use them for other things, such as storing contacts and calendars. It will also help you cut smoking, since it will requisition the cigarette-lighter socket for power.

Most satnav systems can not only show you where you are, and work out a route between any two points, but also recalculate the route on the fly if you either take a wrong turn, or are forced in to roadworks. Add to this realistic-sounding voices - a choice of female or male - and you have, well, not the spy in the cab, but the navigator in the dash.

Plus points you should look for include touch-sensitive screens, recognition of several stored destinations, and plenty of memory to store big maps. If you're driving to the Continent you'll either need to carry lots of CD-roms, or update your handheld on the way. (For the latter, you can buy "expansion chips" able to hold 64Mbyte of data. They are pretty cheap, and a worthwhile purchase.)

GETTING KITTED OUT

Pre-installed or dealer-fitted

VC KD-NX1R
Based on a conventional CD tuner, so it will plug in to all standard dash slots. Costs about £1,050 installed; but the small display is limited to simple arrow commands.
JVC: 0208 208 7654 or www.jvcmobile.co.uk

Alpine
Offers screens that unfold from the fascia stereo slot and uses a DVD player for mapping. Installed, costs £1,800 to £2,600.
Alpine: 0870 3333 406 or www.alpine-electronics.co.uk

VDO
Offers a standalone system using separate dash-mounted screens. The MS5500 DVD-based system costs £1,700 installed. The MS3100 costs about £900 and is a basic package with a 9cm monochrome monitor. It works independently of your stereo, and can go under the driver's seat; the monitor is dash-mounted and easily removed.

VDO Dayton: 0121 326 1162 or www.vdodayton.com

Do-it-yourself

Garmin StreetPilot III deluxe
Costing £850, it offers the same as a fixed system, with a smaller screen. Powered from the cigarette-lighter, it is easily swapped between cars.
Garmin: 01794 519 944 or www.garmin.com

TomTom Navigator
This is a GPS system plus software for Windows PCs for upload to a PocketPC, Palm or Psion. Very usable; updated maps available from the website. Latest version uses Bluetooth, which eliminates wires. Prices starts at £500 including a PocketPC; half that without.
TomTom: www.tomtom.com

Navman
Similar to the TomTom. You will need a Windows PC to transfer the maps. New version also includes Bluetooth, and is powered by batteries. Prices start at £300 for gear; the mapping software costs the same. Handheld is extra!
Navman: www.navman-europe.com

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