Thomas Hardy set some of his novels in Egdon Heath, a fictional area of uncultivated land, and used the landscape to suggest the desires and fears of his characters. He is delving into matters we all recognise because they are common to humanity. This is surely an act of exploration, and into a world as remote as the author chooses. Explorer and travel writer Peter Fleming talks of the moment when the explorer returns to the existence he has left behind with his loved ones. The traveller ‘who has for weeks or months seen himself only as a puny and irrelevant alien crawling laboriously over a country in which he has no roots and no background, suddenly encounters his other self, a relatively solid figure, with a place in the minds of certain people’.

In this book about the exploration of the earth’s surface, I have confined myself to those whose travels were real and who also aimed at more than personal discovery. But that still left me with another problem: the word ‘explorer’ has become associated with a past era. We think back to a golden age, as if exploration peaked somehow in the 19th century – as if the process of discovery is now on the decline, though the truth is that we have named only one and a half million of this planet’s species, and there may be more than 10 million – and that’s not including bacteria. We have studied only 5 per cent of the species we know. We have scarcely mapped the ocean floors, and know even less about ourselves; we fully understand the workings of only 10 per cent of our brains.

Here is how some of today’s ‘explorers’ define the word. Ran Fiennes, dubbed the ‘greatest living explorer’, said, ‘An explorer is someone who has done something that no human has done before – and also done something scientifically useful.’ Chris Bonington, a leading mountaineer, felt exploration was to be found in the act of physically touching the unknown: ‘You have to have gone somewhere new.’ Then Robin Hanbury-Tenison, a campaigner on behalf of remote so-called ‘tribal’ peoples, said, ‘A traveller simply records information about some far-off world, and reports back; but an explorer changes the world.’ Wilfred Thesiger, who crossed Arabia’s Empty Quarter in 1946, and belongs to an era of unmechanised travel now lost to the rest of us, told me, ‘If I’d gone across by camel when I could have gone by car, it would have been a stunt.’ To him, exploration meant bringing back information from a remote place regardless of any great self-discovery.