There are 25 million addresses in Great Britain and by the end of next year Ordnance Survey will be able to tell you where any one of them is - to an accuracy of within four inches. Address-Point will be the ultimate computer address book, provid ing a standard list of postal addresses and their locations for use by local authorities, government agencies, emergency services, marketing organisations, cable television companies and anyone else who needs an accurate specification of all the addresse s in aprescribed area.

OS employs 800 field staff to measure the changing topography of the country. While previously its remit covered roads, tracks, level crossings, slag-heaps and the myriad other features displayed on OS maps, it now extends to defining the grid reference of individual postal addresses.

At the end of 1993, 4 million addresses had been charted. Another 12 million will have been added by the end of this year, and the task will be complete 12 months later when each postal address will have its own 18-digit OS Address-Point reference. The information contained in those digits includes an accurate grid reference, and a date and time stamp to chart changing uses of a building. OS will update the information every six months.

With a new British Standard, BS7666, introducing rigorous standards for a national street gazetteer, a land and property gazetteer and addresses for utilities and Royal Mail, Address-Point is staking its claim to become the standard address list for the whole country.

Because of pressure from potential users, OS decided to bring the product to the market before the project covered the whole country. It has already sold data to the police and fire services in some areas and is confident that other emergency services will find the information indispensable.

Available on CD-rom, 9-track magnetic tape, floppy disc, UNIX cartridge or DAT, Address-Point is licensed to users for an annual fee equivalent to 9p per address.

OS is now identifying value-added resellers of the product. The good news is that taxi-drivers will always be able to find your address; the bad news is that insurance sales men and estate agents will also target you with impeccable accuracy.