Last year I went travelling with my new partner. She was petite, stylish and easy on the eye. She seemed so well informed, too. Every time I made a mistake, she was able to put me on the right track. In fact, I just couldn't stop looking at her, or consulting her.

But the scales soon fell from my eyes. She was always running out of energy, for one thing: for another, she kept leading me up someone else's garden path.

On a filthy night in Dorset, she got my car wedged between two hedges in a steep muddy lane leading to a piggery, having assured me it was a short cut to Toller Porcorum. Enough was enough. Next day she was back on the shelf.

Ten-wheel lorries jammed up bridleways, coachloads of pensioners bumping across stubble fields, the man who drove up the stairs and into the gents ... What humiliating and dangerous tricks have satellite-navigation systems not played on us, the over-trusting and frankly lazy travelling public?

How on Google Earth have we allowed ourselves to favour such anaemic purveyors of half-truths and quarter-facts over the Ordnance Survey maps and atlases, plump with facts and knowledge, redolent of our rich heritage of national culture and history, that have so brilliantly sustained and informed for more than 200 years?

It was Mary Spence, president of the British Cartographic Society, who released this particular cat among the pigeons last week when she addressed the annual conference of the Institute of British Geographers in London.

She told the conference: “Corporate cartographers are demolishing thousands of years of history - not to mention Britain's remarkable geography - at a stroke.” Ms Spence took as an example the Google map of the Winterbourne Stoke area of Wiltshire, which fails to advise travellers that they are in the vicinity of a rather special heap of old building materials: Stonehenge.

There are two pitfalls here, one less serious than the other (though not for its victims). The propensity for sat-nav systems to send us up a gumtree or over a river cliff is partly about computer-based techies creating maps without ever leaving the comfort of their nice warm screens to check out, in the real world, what they're advising us to do in the virtual one; but it's also our own silly fault for not paying attention and using a bit of common sense.

I wouldn't have got those Dorset hedgerow scratches if I'd heeded the still small voice that whispered, “OK, this is mud and not tarmac, and that is the sweet essence of Large Whites coming in at the window, so why don't you just back up and cut your losses before ...”

Far more threatening to our national sense of self - and, more importantly, to our edification and pleasure - is the notion of driving or bicycling through a landscape represented solely by blue, green, orange and white lines that knit together only blank grey spaces. (I say nothing of walking, because you wouldn't get farther than the first stile.)

Lay the Google and OS Explorer maps of the Stonehenge area side by side. On Google - roads, a river, a ghostly hint of buildings, a flat land. That's it. On the Explorer, all round the mighty henge itself: ridged and billowing downland, ancient trackways, processional paths, long barrows and tumuli where our lordly ancestors lie buried, the mysterious banking of the Cursus track, copses and spinneys bounded by unexplained earthworks, the River Avon coiling past Ham Hatches and Moor Hatches.

Hatches? What for? Why these vast earthworks? Which ruler sleeps under King Barrow? Who raced the 5,000-year-old straights of the Cursus? I can go to Google - the fantastically useful, unbelievably knowledgeable Google search engine, I mean, not the pallid Google pseudo-maps - and find out all I'll ever want to know.

But I'd never have suspected the presence of this dense palimpsest of history - my own, my native history - if the OS map hadn't told me, in its dry, economical, factual, absorbing, catalytic way, of its existence.

Do we need all this stuff to get from Amesbury to Winterbourne Stoke? No, we don't. Should we delight in it, and feel grateful to be part of it, and smack our imaginative lips over it, and be inspired to come back and explore it with a flower book and an archaeology book on a sunny day pretty soon?

Absolutely. That's our national heritage, delivered a little elliptically but with a poetic fitness for purpose by Ordnance Survey, our priceless national treasure.

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