A replica world is a dangerous place in which to live

The future has no sense of humour. What begins among us as a joke will end up with our great-grandchildren as a sermon. They, in turn, will look back on us with wide-eyed horror because our jokes were so callous. Laughter heard across the centuries has a skull-like echo.

Here is the fate of a funny story about maps. It began as a joke, but in the course of a century turned into a sinister parable. I found it in three successive fragments which I came across by three different chances. The first one comes from a book published in Paris in 1884, an anecdote told to his daughter by an old Polish officer who had served in the Turkish army around the time of the Crimean War.

After the Treaty of Unkiar-Skelessi in 1833, between victorious Russia and defeated Turkey, a Turkish delegation went to St Petersburg to ratify the treaty and complete its details. In particular, they had to demarcate the new border which gave up to Russia the land of Abazia (now Abkhazia) on the eastern shore of the Black Sea.

But map-reading was beyond these Turkish dignitaries - something they left to foreign underlings. In their hotel room they stared at a marked map of Abazia, and could make little of it. Next to it, though, somebody had left a large-scale plan of the Tsar's private park. The grandees compared the two maps and - having no notion of cartology - concluded after measurements taken with a piece of string that Abazia was not much bigger than the imperial gardens in St Petersburg. A walk in the park confirmed their opinion; the Sultan would lose nothing by giving up such a paltry scrap of territory. They signed. When the Sultan found he had abandoned a province as big as Wales, it was too late.

I don't believe that story. It has a folk-tale feel about it; a joke repeated about different people at different times. But it obviously circulated, and in 1893, when Lewis Carroll wrote his last book for children, that anecdote of the Turkish map was somewhere in the back of his head. In Sylvie and Bruno Concluded (a lame effort, without the confidence of the "Alice" stories written over 20 years before), a comic character called Mein Herr reveals that he has devised enormous maps, "... a hundred yards to the mile. And then came the grandest idea of all! We actually made a map of the country, on the scale of a mile to a mile!"

He goes on to explain that the idea failed. "The farmers objected; they said it would cover the whole country and shut out the sunlight. So we now use the country itself, as its own map, and I assure you it does nearly as well!"

Nearly half a century later, the image of the 1:1 map turns up again in a sketch by Jorge Luis Borges called "Of Rigour in Science". It's written in an archaic prose style, and Borges says that it was composed by a certain Suarez Miranda of Lerida in 1658. But that is the sort of trick he often played on readers. The truth is, I suspect, that as a child in Buenos Aires he had an English nanny who read him Lewis Carroll, and in particular Sylvie and Bruno.

The Miranda/Borges story is only about 300 words long. It describes how, in a nameless empire, there grew up a school of cartographers so expert that they produced a map of a province large enough to cover a whole town. Finally, they "drew up a Map of the Empire which was done to the same scale as the Empire itself, and which coincided with it at every point." Then, as with Lewis Carroll, the idea turns out to have overstretched itself. Later generations, "less absorbed in the Study of Cartography", grew bored with this useless mega-map and let it fall into decay. Now, "in the deserts of the West, there survive shattered Ruins of the Map, inhabited by Beasts and by Beggars; in all the Land, no other relic of the Cartographic Disciplines remains".

The humour of these three map stories grows richer but also much darker, as one version succeeds another. I can imagine a 19th-century Parisian telling the Turkish version to laughing, whiskered friends over a good restaurant dinner; it's little more than a yarn about stupid foreigners with a flavouring of map-metaphysic. But the second version, though it comes from a poor book, shows Lewis Carroll's philosophi-cal wit at its most dangerous and unsettling.

Carroll is the writer who invented the phrase "as large as life and twice as natural" - pretty apposite to these total maps. Here he produces the idea of using "the country itself as its own map", a jest which goes to the heart of our own post-modern arguments about what is real and what is image. And Borges pushes the fancy even further. All attempts to substitute a dummy world for the real one, he seems to say, will soon fail and shrivel away to a few haunted ruins.

This brings us to our own strange world, in which the fake and the simulation grow so large that they cover the things they imitate. To see what I mean at its logical extreme, imagine a television historical documentary series which expanded to become a 1:1 map of the past. Imagine the old World at War series being remade in a version which lasted for six years of continuous viewing. That seems insane. And yet it is only the fantastic ultimate destination of a path which we have already begun to explore.

The "heritage industry" often attempts to do something of the same kind. Society - or the laws of the market, if you like - decided that a museum colliery worked by actors was preferable to a pit where human beings won coal to burn in grates or furnaces. Not everything is wrong about these Jurassic Parks for extinct forms of labour; the social historian Raphael Samuel is right to point out that thousands of visitors enjoy these places and learn from them. But theme parks cannot be more than maps of what has passed away. If they pretend to be more, then their hubris grows dangerous. If the map-scale grows so ambitious that every house and hedge becomes visible in sharp relief, and that the line which marks a road develops into a pale band dotted by men and horses, then the original landscape beneath the map begins to become superfluous.

It is all about control. It's another episode in the long human struggle to eliminate everything unpredictable. In that struggle, the most powerful weapon is imagination. Virtual reality is more reliable than the non-virtual kind.

On the great map, no river bursts its banks and no tree sheds leaves - unless the cartographers decide to change their artwork. In the great museum, the dockyard sawyer never cuts his finger and the child in the threadmill never weeps from the pain of her chilblains - unless the script is altered. And the new historians write books which commemorate commemorations, thus avoiding the doubts which can jump out from behind actual events and real people to ambush the scholar. Take Joan of Arc: it is the statues of her, and the speeches of the politicians who unveiled them, that are now held to matter. The awkward woman who once lived, and all her visions of her France and her God, can be left - thankfully and a touch scornfully - to the historical novelists.

But the giant map begins to tatter as soon as it covers the empire. Lewis Carroll warned that farmers - those who live by light - would have none of it. Borges knew that all reproductions are static, and therefore grow boring and unfashionable within a few years. The sheer unreliability of life means we can never become the authors and directors even of our own dreams - let alone our own lives. But it seems that we will go on trying.