In the 19th century a considerable amount of military manpower was used to draw detailed maps of the British Isles. Updated regularly ever since, this valuable intellectual property is owned by Ordnance Survey and protected by a tiny, but intentional flaw in each map that identifies copies. But the road maps based on the data have become cheap commodity items. The challenge for personal navigation device maker TomTom is to avoid that fate.

The attempt is not going well. TomTom shares lost another 10 per cent on Tuesday morning following a trading update. The Dutch group has now seen its market capitalisation shrink by two-thirds from its October high. The problem is rapidly falling prices. Nervous about the outlook for consumer spending, electronics retailers have been clearing inventory, as have some smaller map device makers. So while unit sales unit sales for the satnav market doubled in North America in the first quarter, compared with 2007, and grew by 40 per cent in Europe, TomTom’s revenues actually fell. Margins collapsed, and full year guidance for sales has been cut by a tenth.