The past 20 years have seen huge price rises in antique maps, says leading London-based dealer James Rutter (www.mapmogul.com), because of the decline in the number of them on the market. "Typically, prices have doubled for standard items, and exceptional items have appreciated by up to 10-fold. Decorative maps by famous 16th and 17th century cartographers such as Speed, Blaeu and Ortelius are always in demand. Generally, the earlier the better, with exceptions for rarity. The earliest obtainable maps date from around 1540, and the biggest market is for maps of the world and North America. Those with mythical islands and other 'fancies' are true collectors' items and fetch top prices."

London is the hub of antique-map dealing, reportedly with more dealers than the whole of the US. Old maps were produced mainly in Europe and most of the stock is still here, with the British enjoying the biggest map-collecting culture. A 1570 map of the world by Ortelius, valued at £1,300 in 1987, has been fetching £5,000 in recent years. And a Speed world map from 1627 selling for £2,200 in 1986 is now worth more than £10,000. Last year the 1507 map by Waldseemuller which first gave America its name was sold at Christie's for £545,600 - a world record auction price for a single-sheet map.