GUEST BLOG: By Airship to the West Pole - Ian McDonald

In the business of creating parallel Earths, I've always been tempted towards alternative geography rather than alternative history. Changes in minor details of who won what American Civil War battle, do not make for a particularly thrilling alternative world (well, not for me). Sometimes, alternate history can give me that right and proper wait . . . where am I? chill, which in my book, is the chief pleasure of alternate world fiction: things are not as they seem – the world is a little bit queered. Ian MacLeod's The Summer Isles did it for me. In it, Britain loses the First World War and therefore becomes the country that suffers hyperinflation and the rise of fascism as opposed to Germany. But I'm not a history wonk and details of battles and generals (and Points of Departure – an expression I hate) seem to play too much to the Great Man approach to history.

I like broader brushes, bolder strokes for my alternate worlds. So, in Planesrunner, we have – or will have – a world where Britain (not Ireland, I hasten to add) is an island at the mouth of the Mediterranean; and we’ll also have a parallel Earth without usable mineral oil. Call me a determinist, but I'm interested in what kinds of worlds and societies can rise within those constraints – or with those opportunities: alternate geography. I've got most of the Nine (Ten, including our world) Worlds of the Plenitude mapped out. I may never use them, but I like to know what they're like, in case I ever do (and I do have the mechanism of the Plenitude of Known Worlds moving its headquarters every six months as an excuse for a little inter-plane sightseeing).  Earth 1 is verboten (though, fiction being fiction, nothing verboten ever successfully stays verboten, and it pops up in Be My Enemy, Book 2 in the series), Earth 2 has Britain-off-the-Med, Earth 3 is Captain Anastasia and Sen's coal-fuelled electropunk world, Earth 4 is like our world – but with the significant difference that in 1964, the alien Thryn Sentiency colonised the far side of the moon and transformed it into an enormous alien mechanism; Earth 5 has five humanoid species as opposed to our one, and Earth 6 . . .

To writers, there's no such thing as idling, doing nothing, dicking about on the internet. It's creative hiatus. The reason the best ideas come in the shower is because you're not thinking about them. Your senses and mind are occupied elsewhere, so the pressure is off. Sometimes, like spying djinn, you have to look away to catch sight of what you really want to see.  I was twiddling around on Google Earth, when my fat fingers did something and spun the globe so that the north pole was in the centre of the Pacific, around about where Tahiti is. A West Pole, so to speak. Ooh, I thought, what an interesting planet we now have. And, what an interesting idea for a parallel Earth – there's been a pole shift (wave hand over the process, we'll deal with it if we need it) and the world has been turned 90 degrees on its side. This is a game you all can play by the way. Have this happen in prehistory, so that the settlements and migration patterns of the planet turn out very differently.

What's immediately obvious in this alternate world, is that the world is divided into three bands: the great Northern Polar Ocean – our Pacific; a great Southern Ocean – broken by the bulk of Eurasia leading towards the south pole; a Central Ocean – our Arctic Ocean, with Greenland as a lush equatorial paradise; and then a great band of continents and land mass around the middle of the world. North America, arcs up from Alaska in the East to California in the polar regions, while the magnificent sweep of South America, lies along the equator, the centre of the world. Then, to the west, the tropical island continents of Antartica and Australia appear. West of Australia, the sunset islands of  the archipelago of Indonesia and Melanesia, then Sri Lanka in the frozen south to the icebergs of Fiji make an arc of the entire planet. To the west of the archipelago is the massive landmass of Asia; Europe in the chilly south. Africa is an Arctic continent: the massive, frozen south. Try it. It's easy, and a fine mental exercise: The world turned on its side. Now, imagine that the climate patterns and jet streams follow the spin of the planet. Where are the rainforests, the deserts, the breadbaskets? The Andes becomes a massive equatorial cordillera along the northern edge of South America. The mountains of Antarctica are lush and forested, the high plateau a great desert.

How would history play out across a geography like this? It would be different from that of our world at every point. Where would the empires have risen? The developers of agriculture, metallurgy, printing and information? What is the influence of geography on the history of our world? Once you start, it's hard to stop. And this is a world I may never even visit in any detail (though the temptation is, having put all the head-work into it, to wrangle things around to get to use it). Creating an alternate reality is about looking at the world on its side. From a different angle, and asking how things might work differently, and from that, thinking about how things work now. That's the fun of alternate worlds – they force us to look at our own world with fresh eyes.