This festive season, why not make a gift of a charming antique map of a disaster zone? Herefordshire, for example, is going cheap. London map dealer Graham Franks has no complaint against the county's inhabitants, nor those of his lesser 'disaster zones' - Bedfordshire, Merioneth, Flint and Denbighshire - except that they do not buy old maps.

'You'd think Herefordshire was diseased,' he joked as he pored over engraved decorative maps for Sotheby's sale next Tuesday at 10.30am, 'but I'm sure I saw some people last time I was there.'

If the price of pre-1850 county maps is a barometer of national prosperity, we had all better emigrate. Dealers are unanimous that, compared with the rest of the print trade, they have long been underpriced.

Maps that sell best, according to Mr Franks, who trades internationally by mail order, are of places with strong national identity - Japan, South-East Asia (notably Taiwan and Korea) and North America. Italy was a disaster zones until five years ago, when its unconventional economy began to yield spare cash. France, surprisingly, is a 'bad place', although Britanny and Corsica are saleable.

'Norway?' I ventured. 'Hmm. The trouble with Norway is that it's a stupid shape and has Sweden stuck next to it,' he said. 'Not a lot you can do about that.' Iceland sells. Even Antarctica sells. So what of poor bloody Herefordshire?

Jonathan Potter, the New Bond Street map dealer, equates county map values primarily with property values - people can afford to push up prices. Dealers agree that Surrey, heaving with well-off professionals, is a top seller, while prices for Suffolk and Norfolk maps have fallen as the tide of property-buying commuters and weekenders has retreated. Herefordshire's property values are stagnating - and, as Richard North explains on page 33, its very future is in doubt.

But property is not the only determinant of price. Maps of Cornwall sell for almost as much as those of Surrey, although Cornwall has a population of only 481,000 (compared with Surrey's 1,002,000) and modest house prices. The explanation is not only that everyone loves romantic Cornwall, with its memories of bucket-and-spade holidays, but that the county is bounded by sea - in which cartographers' sea monsters and mermaids frolic, and the sails of galleons billow. Herefordshire, land-locked and square, offers little scope for such flourishes.

London's leading dealer in antique maps, Raymond O'Shea, cites new motorways as dispersers of map buyers, especially the M25, which has contributed to the rise in value of maps of Buckinghamshire, Berkshire, Kent and Essex.

The most under-appreciated county maps are of Middlesex. Most gift-buyers will be unaware that, prior to boundary changes, Middlesex embraced salubrious Hampstead and Chiswick and reached as far as Waltham Abbey, Uxbridge, Staines, Weybridge and the Isle of Dogs.

According to the property-values criterion, Middlesex map prices should outstrip all others. But the Greenwood brothers' big 1834 map of Middlesex, despite its handsome vignette of St Paul's Cathedral, retails for a modest pounds 120 or less, compared with pounds 160 for their Surrey.

A highly decorated, uncoloured Herefordshire map of 1610 by John Speed, the most famous name in map-making, will probably cost pounds 400, while Surrey and Middlesex from the same edition will cost pounds 1,200 each. A tiny A4-size 1836 map of Herefordshire by Thomas Moule, much loved for his vignette views and portraits, would cost pounds 50, Surrey of the same edition pounds 150, Middlesex pounds 120.

It pays to compare dealers' prices, and to look for maps at junk shops and book fairs. There is a monthly antique map and print fair in London. Beware of inflated prices in general antique dealers' shops.

Some mail-order firms offer value for money: the catalogue of Postaprint Iver Heath, Buckinghamshire, offers a 1787 map of Surrey by John Cary for pounds 48 (shop price: around pounds 120) and his Herefordshire for pounds 18 (shop price: around pounds 40). It prices an 1836 Surrey by Moule at pounds 70. An advertisement by London map dealers Tooley Adams in the Map Collector offers a Herefordshire by Robert Morden, a late- 17th-century map-maker, at pounds 22 (shop price pounds 75).

Mail-order prices invite inquiries about condition. In map collecting there is no equivalent of the 'fine'/'very fine' grading systems of stamps and coins. Condition is a matter of taste. Steve Luck of Tooley Adams says that some collectors prefer a plain to an originally coloured map by the Greenwood brothers because, bound in a book for 160 years, the colour offsets on to the opposite page, turning brown as it seeps through the paper.

His personal preference is for slightly grubby, finger-marked maps - the same brand of connoisseurship which has put a value on the patina of furniture. He tells American collectors showing distaste for browning, wormy, 400-year-old maps: 'You'll be lucky to look as good as that in four centuries' time'.

Whatever cachet grubbiness now confers, the fact is that the supply of loose maps has dwindled and collectors are having to accept poorer quality. Catherine Slowther, of Sotheby's map department, points to three folders of loose maps awaiting sale and says that, seven years ago when she joined the firm, there would have been 20 or 30 of them. Collectors of loose maps have graduated to atlases and dealers now think twice before breaking books.

That raises the biggest mystery of map collecting: why prices of loose maps remain stubbornly on the floor. Saleroom prices have been creeping up by an unremarkable 10 per cent a year for the past three years as auctioneers have applied a ratchet to estimates. Even this modest buoyancy is looked upon as a sellers' market. It is of no interest to speculative buyers - too little profit in exchange for too much homework.

The fact is, this is as yet a very 'imperfect' market. It pays to shop around. And there are, after all, fewer than 500 members of the London-based International Map Collecting Society spread throughout 54 countries. Hardly enough to generate a bull market. Graham Franks, relishing the paradox, said: 'If maps were more common they'd be worth more - because you could generate more collectors.'

Monthly antique map and print fair, Monday December 13 (9.30am-7pm): Bonnington Hotel, Southampton Row, London WC1 (0242 514287). The Map Collector quarterly (0442 824977); International Map Collectors' Society (081-769 5041); Sotheby's (071-408 5291); Postaprint (0895 833720). London and provincial dealers: O'Shea Gallery (071-730 0081); Jonathan Potter (071-491 3520); Graham Franks (071- 405 0274); Tooley Adams (071-240 4406); InterCol (081-349 2207); Warwick Leadlay (081-858 0317); Avril Noble (071-240 1970). Oxford: Magna Gallery (0865 245805). Chester: Richard Nicholson (0244 336004). Edinburgh: Carson Clark (031-556 4710).

Map prices by county and mapmaker

Artist Hereford Surrey Middlesex

Speed, 1610 pounds 400 pounds 1,200 pounds 1,200

Speed, 1676 pounds 320 pounds 800 pounds 800

Morden, 1695 pounds 75 pounds 175 pounds 150

Cary, 1787 pounds 40 pounds 120 pounds 80

Greenwood, 1834 pounds 60 pounds 160 pounds 120

Moule, 1836 pounds 50 pounds 150 pounds 120

(Photograph omitted)