THE MAN WHO PAYS HIS WAY: Do you know where you are now?

Coca-Cola is said to be the world's most recognisable brand. It is also the name of a bus station in the Costa Rican capital, San Jose - not because the makers of Coke have taken to sponsoring transport termini, but because there was once a large "Coca-Cola" sign in the vicinity. Even though it has long faded away, everyone calls the bus terminal - and, by extension, the area around it, Coca-Cola.

Things go better when you know where you are. That is the theme of a fascinating exhibition which opens this morning at the Design Museum near Tower Bridge in London - at least I think it's near Tower Bridge; to tell you the truth, I got a bit lost on my way there. I should have taken my A to Z.

Seventy years ago, the writer and artist Phyllis Pearsall found herself hopelessly lost in London. When she finally worked out where she was, she went for a walk - for an estimated 3,000 miles while she catalogued every one of the city's highways, roads, avenues and culs-de-sac. Even after this heroic performance, Ms Pearsall could not find anyone prepared to publish the results. So she started her own firm, Geographers' A-Z Map Company.

This is one of the tales told in the exhibition, "You are Here". The curator, James Peto, has assembled an impressive collection of designs "to help us understand the world we live in and to negotiate our way around it".

In travel, there is no finer device for finding your way than Harry Beck's London Underground map. It reduces a complex network set in the chaotic geography of western Europe's largest city to a clear, manageable diagram.

Of course the Tube map is rubbish if you want to find, say, Soho or Mayfair - neither of which is mentioned on the map - or wish to walk on the surface from Shoreditch to Bethnal Green, which may appear adjacent on the map but are a unpleasant mile apart. James Peto has found that the Underground map shapes foreign visitors' views of the capital. He says he understands the local geography within a 10-minute walk from a Tube station, "but not necessarily how these areas fit together".

EVERY MAP distorts reality: one exhibit shows how applying Mercator's Projection to a picture of a man creates an elasticated image with comically exaggerated head and feet, and an implausibly narrow waist. Designers' intentions are mostly good, though, as they strive to unravel the world for the benefit of the traveller. One well-meaning cartographer, John Sims, has come up with an Upside Down Road Map of Great Britain. This is intended to help those trying to drive from John O'Groats to Land's End - though if you can't manage the conventional map of the nation, perhaps you should go by train. Rail is the mode of choice for many blind travellers, and You are Here includes a Braille rail chart of Britain's network.

For sighted travellers to Japan, individual railway maps even show you where to sit on the train in order to be closest to the exit at your destination station. When you arrive and try to track down a particular location, you will find Japanese addresses are numbered according to a system impenetrable to most outsiders. Handily, cartographers have done their best to help travellers by producing street maps with pictures of individual buildings on them.

A HANDSOME circular Air Age Map of the World is centred on Heathrow, with interesting effects on the fringes: New Zealand is absurdly contorted and almost fills a quadrant. Many travel companies regard maps as marketing opportunities, and this one was sponsored by BOAC (the long-haul predecessor to British Airways). It is revealing how many destinations, such as Santiago in Chile and Belize City, have long fallen off the map.

Finnair tried something even more ambitious 30 years ago, constructing an extraordinarily convoluted route diagram that also carries, in the smallest of print, the precise schedules of the Finnish airline - down to the type of aircraft. In three decades of aeronautical progress, it is interesting to note that it now takes longer to fly from London to Helsinki than it did in 1975.

THOUGHTFULLY, JAMES PETO has included a nautical chart of Southampton Water, the Solent and the Isle of Wight, possibly for use by passengers and crew who have signed up for a round-the-world cruise aboard the Aurora.

One neat piece of cartography that the curator was not able to include, because it resides in a museum in Erfurt in the former East Germany, is a globe (see above) produced by the German Democratic Republic. The makers faced a problem: what to do about West Germany, the bigger, richer and more powerful neighbour? The solution: to bind the globe with a seam that just happens to shrink the Federal Republic and to obscure attractions from Lubeck to Lake Constance.

You are Here: Where is it?

At the Design Museum, Shad Thames, London SE1 2YD (0870 833 9955; www.designmuseum.org). Nearest Tubes (I think): Tower Hill, London Bridge and Bermondsey. The museum is open 10am-5.45pm daily, admission pounds 6