The Long Earth is a phenomenon explored in (unsurprisingly) The Long Earth. Imagine a pack of cards. Our world- Roundworld, Datum Earth, it goes by many names- is in the middle, and one can travel, using the Stepper, through the cards, although one often experiences nausea. Hardly any of the worlds are occupied, so it seems the evolution of mankind is a unique thing. It is unknown whether the card pack circles round to meet itself, or whether there is something more mysterious at the end. However, as one travels further from Datum Earth the differences become more pronounced, with worlds in the ten-millions having a much greater chance of being uninhabitable than the closer ones, and one starts to find large sections of "purple scum" worlds where no complex life exists. By the two hundred millions one finds Earths which have different levels of gravity, and it has been speculated that there may be a world where Earth never existed at all.
Datum Earth is one of many 'interglacial' worlds; that is, worlds that are covered in trees and rich forms of life. Animals thrive there, with unusual species of armadillos and horses being in profusion. Who knows, there might be a Hermit Elephant in there. The interglacial worlds are surrounded by a set of worlds experiencing ice ages- this is called the Ice Belt, and it starts at West 11. As a result the previous world, West 10, has become a sort of 'mustering' world, where supplies and suchlike can be purchased.
Similarly there is the Mine Belt, a set of worlds filled with desolate deserts and rich minerals, and the Corn Belt, which is good farming country and is ideal for setting up colonies. It starts at West 100,000 and extends to around West 460,000 or so.
There are some worlds that are mere dust-bowls, like the worst class of planets, or are covered in ice, where nothing can grow. These are called Joker Worlds, and are not to be confused with the other Jokers. Diamond Worlds also exist: these are places of truly outstanding potential, for one reason or another, and create excitement for what they represent. Rectangles is one, as it carries evidence that there was once a technological civilisation here way in advance of Datum Earth. But the fact its people all died out might just conceivably be related to an awful lot of smouldering radiation...
Belts of Earths, and notable Earths
- The Low Earths, Earths less than about 100 (?) steps away from Datum Earth.
- The Ice Belt, starting from West 11 and extending to about West 36,000.
- The Mine Belt, covering West 36,000 to West 100,000.
- The Corn Belt, covering West 100,000 to about West 460,000.
- West 100,000, also known as Good Old Hundred K.
- West 101,752: contains New Scarsdale, a "county seat", the "county" in question spanning several worlds, and including Reboot.
- West 101,754: the world on which Reboot was founded.
- West 141,759: a world under quarantine.
- West 191,248: a slightly shop-soiled Long Earth.
- West 389,413
- Cueball: a perfectly smooth copy of Earth, hence the name.
- Unnamed belt, from West 460,000 to West 1,000,000.
- The High Meggers, from West 1,000,000 to some way past the Gap. Includes subregions such as the Valhallan Belt.
- West 1,176,865
- West 1,217,756: location of New Springfield.
- West 1,349,877
- West 1,397,426: location of Hell-Knows-Where.
- West 1,400,013: the location of the settlement of Valhalla.
- Happy Landings is somewhere around here.
- West 1,617,524: The home Long Earth of the Beagles.
- West 1,617,848
- Gap Minus One: the nearest Long Earth to the Gap, a little bit past West 2,000,000.
- The Gap: strictly speaking the first Western Gap, but everyone just calls it the Gap. Later used as a point of entry to the Long Mars.
- First Person Singular is somewhere on the West side of the Gap.
- Unnamed belt up to approximately West 30M. A crustacean-dominated subbelt exists, centred on West 17M or thereabouts.
- West 17,297,031: contained a society of crabs, complete with buildings and palace.
- Purple Scum Belt 1, from a bit before West 30M to around West 100M. Seventy million worlds that don't contain any life more complex than single-celled bacteria, though one presumes there are a few exceptions in there.
- Pangaean Belt, a subbelt of the first Purple Scum belt, from about West 35M to about West 50M. Notable for supercontinents, very low oxygen levels and high carbon dioxide levels.
- West 35,693,562: a typical Pangaean Belt world consisting of a single supercontinent, the interior of which is too dried out to support life at all.
- Cnidarian Belt, from a little past West 100M to about West 110M.
- West 102,453,654: a typical Cnidarian Belt world.
- Purple Scum Belt 2, from West ~110M to West ~130M.
- Anaerobic Belt, from West 130M to about West 161M. Worlds in this belt contains no oxygen-producing life, and hence no oxygen.
- Unnamed belt, West ~161M to West ~182M. The first half of this belt is dominated with acid-based life; the second half contains many worlds where the amount of land is much higher or lower than the Datum, and a few more examples of "Traversers" similar to First Person Singular.
- West 161,753,428: one of many worlds within the belt that contain acid-based life.
- West 174,827,918
- Bonsai Belt, West ~182M to West ~190M. Another belt consisting largely of dual-origin life.
- West 182,498,761: a typical Bonsai Belt world.
- West 182,674,101: the location where the Neil Armstrong I crashed.
- West ~190M to West ~210M: another purple scum belt.
- West ~210M to West ~220M: another Anaerobic Belt.
- West ~220M onwards, where there are Gaps all over the place, and the number of moons Earth has keeps changing, as does the gravity. It is believed that this is due to the process of Earth's formation occurring differently in these worlds.
- West 239,741,211 a.k.a Karakal.
- West 247,830,855: where Earth is merely a moon of a larger planet.
- West 250,000,000: the furthest Western world visited by the expedition of 2045. The commemorative cairn here is bigger than the Chinese one on East 20,000,000.
- Earths East of the Low Earths. If these worlds are also divided into regions, the names of these regions are unknown.
- East 2,201,749: contained a complex ecosystem that was predicted to be wiped out by a hypercane between visits.
- East 2,217,643: the first Eastern Gap, discovered by the Chinese expedition of 2040. The fact that Datum Earth lies close to halfway between both Gaps probably says a lot.
- East 8,616,289: home to what appears to be a society of tortoises.
- East 20,000,000: the furthest Eastern world visited by the Chinese expedition. Contains a commemorative cairn and not much else.