By JANE FRYER

Last updated at 10:30 01 February 2008

Your'e looking at the oldest surviving map of Britain, dating from around 1360.

And, give or take a bit of poetic licence north of the border, it's startlingly accurate.

There are the Severn, Thames and Humber, the loop of the Wear in Durham and the Thames estuary, all easily recognisable.

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As are the more than 600 cities, towns and villages, almost 200 rivers, and a rudimentary road network marked with thin red lines and extending to some 3,000 miles.

Along with countless hills, mountains, lakes, forests - New Forest and Sherwood - and even Hadrian's Wall, labelled with its popular name, murus pictorum, the Picts' Wall.

The significance is enormous, as a new book reveals.

"It is the first modern map of Britain and the oldest surviving map which shows the coastline in recognisable form," says author Nick Millea, map librarian at Oxford University's Bodleian Library.

"All previous maps gave a theological interpretation, showing how Britain fitted into the Christian world.

"The Hereford Mappa Mundi from approximately the same time has Jerusalem as the centre of the world.

"Geography just wasn't important."

Named after topographer Richard Gough - who bought it in 1774 for half-a-crown (121/2p) and bequeathed it to the Bodleian Library - the map is drawn in pen, ink and coloured washes on two skins of vellum and measures almost 4ft long by 2ft wide.

Almost as surprising as the detail and the accuracy (if you discount misshapen Scotland) is the startling orientation - the original map was drafted to face east towards Jerusalem, rather than the north, because its topographers had not entirely abandoned their theological way of thinking.

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In its correct position it looks rather like an old mildewed boot with Wales as the heel, Scotland as the toe and East Anglia sticking up into the air.

"There are 600-odd places and, if you compare it with a modern map, most of them are in pretty much the right spot," says Millea.

"We don't know whether they did the coastline first then filled in the interior, or whether it was done by word of mouth - a verbal map - so they put in London then worked outwards, adding places they knew."

Nick Crane, topographer and presenter of TV series Map Man, thinks they may have used an astrolabe - a highly technical instrument used by classical astronomers, navigators and astrologers which involved checking the horizon, the stars, the sun and all sorts of angles.

"This could be the beginning of mathematical map-making - some of the points of latitude have probably been measured through astronomy," he says.

But why do they get Scotland so wrong? The Clyde and Forth and Edinburgh are recognisable, but the rest is all a bit of a mess.

"It was created at a time when Scotland was a foreign country and little was known about it so they improvised," says Millea.

"That's why there are so few place names north of the border."

While the map in the Bodleian Library dates from the mid-14th century, experts think it was copied from an earlier map, from around 1280, which didn't survive.

"Geographically, it fits with the time of Edward I. All the castles of his conquest of Wales are there.

"And the few Scottish place names shown were around at the time of Edward I, but not much later."

This may account for a few mistakes. Cardigan Bay is missing.

Cornwall extends too far west, Orkney's too big and Dartmouth and part of central Wales are shown as lakes rather than upland areas.

Lewes in Sussex pops up twice.

But regardless of these errors, the Gough map represents a massive leap forward.

As well as showing the geography, it gives a snapshot of England and Wales at the time and an idea of the contrasting fortunes of places.

Some towns, such as Blakeney in Norfolk which was once a thriving port, are now tiny settlements compared with their apparent importance in the 14th century.

In contrast Manchester appears to be no bigger than Charlesworth, a little village in the Peak District.

The Gough map is one of this country's most important historical documents - it formed the basis for almost all the maps of Britain for 200 years.

And with its green rivers, red-roofed cathedrals, and extraordinary detail, it is surely one of the most aesthetically pleasing.

The Gough Map: The Earliest Road Map of Britain? by Nick Millea. ISBN 9781851240227. £25.