The Disc

The Disc, unlike any other planet in this universe, is flat rather than round. It is approximately 10,000 miles across, about 12 miles thick at the Rim, and much thicker toward The Hub with its mountain ranges. At the centre is the massive mountain (Cori Celesti) standing 10 miles high with the home of the gods (Dunmanifestin) at its peak. Areas toward the Hub are equivalent to Earth’s polar regions, whereas those closer to the Rim are warmer and tropical, since the Disc's sun passes closer to them in its orbit. At the Rim, a great encircling waterfall (the Rimfall) sends the Disc's oceans cascading into space. Directions within the Discworld are not given as North, South, East, and West, but rather as directions relating to the Disc itself: Hubward (towards the centre), Rimward (away from the centre) and to a lesser extent, turnwise and widdershins (respectively, with and against the direction of the Disc's spin).

There are four main continents on the Disc, along with a number of geographical, political regions, and islands, some of which have not been described in detail in the novels. The majority of the Disc's landmass is composed of a single supercontinent, comprising of a large main region and a smaller Counterweight Continent connected by a narrow isthmus.

The Disc rests on the shoulders of four enormous elephants named Berilia, Tubul, Great T'Phon, and Jerakeen. The Disc slowly rotates around its central axis to evenly distribute the load between the elephants, and takes 800 days to complete a full rotation. The elephants are as old as the Disc, established during the events of 'The Light Fantastic'. Disc telepaths have attempted to read the minds of the elephants, who apparently feel "incredibly bored", and have terrible back pains.

The Disc’s small sun and moon (each 80 miles in diameter) have complex orbits that can only be accommodated if, every so often, one of the elephants lifts a leg to allow either one to pass underneath.

There was once a Fifth Elephant who fell to the Disc in ancient times and caused the continents to split and mountains to rise. It also left behind deeply buried fat deposits, which are now a mined and traded commodity by the Dwarves.

Great A'Tuin is the Giant World Turtle (species: Chelys galactica) who travels through space, carrying the four giant elephants and disc on its back. Great A'Tuin's gender is unknown, but is the subject of intense speculation by some of the Disc's finest scientific minds. The sex of the World Turtle is pivotal in proving or disproving a number of conflicting theories about the destination of Great A'Tuin's journey through the cosmos. The "Big Bang" theory speculates that Great A’Tuin is swimming through space to its mating grounds, where the Disc may be crushed in the mating attempts (or simply slide off). The other theory, described as being popular among academics, is the "Steady Gait" theory, that he/she came from nowhere and is going to keep swimming through space to nowhere, forever.

Great A'Tuin has been mentioned to frequently roll on its belly to avoid asteroid and comet collisions, or even to snatch these projectiles out of the sky, which might otherwise destroy the Disc. These stunts do not affect the Disc's population, other than to induce severe seasickness on anyone who happens to be looking at the night sky at that time.