Land of Ooo

The Land of Ooo is the main setting of Adventure Time, and is the home of Finn and Jake, along with all of their friends and foes. It is divided into different kingdoms, of which the most prominent are the Ice Kingdom, Candy Kingdom, Fire Kingdom, Cloud Kingdom and Lumpy Space, which is technically a kingdom, as it has a princess. There are also many geographical areas not known to be part of any kingdom, such as the Evil Forest and the Bad Lands. Pendleton Ward has confirmed that the Land of Ooo is a continent.

Map
Two different official maps of the Land of Ooo were released by Frederator Studios along with the original Adventure Time pitch documents: the seen in the infobox to the right and a  seen in the gallery below. Of these, the black-and-white one drawn by Ghostshrimp is probably more accurate for several reasons:
 * 1) Its general shape matches the aerial view of Ooo seen in "Business Time" (see picture in gallery below.)
 * 2) A slightly modified version of this map appeared on Princess Bubblegum's hologram map in "The Other Tarts".
 * 3) On the black-and-white map, the names of certain places match up with the names used in the show and by its creators, while some of the names on the color map do not.

Post-apocalyptic setting
Pendleton Ward, the creator of Adventure Time, has stated in an interview that the Land of Ooo is actually a post-apocalyptic world, the result of some sort of global disaster, hence the ruined pieces of modern technology scattered across the land. The beginning of the opening sequence briefly shows a wasteland peppered with nuclear bombs and other weapons. (There is also a scarred arm that rises from a tree at the beginning.) This also explains the origins of the frozen Businessmen in "Business Time" and the half-buried car chassis and broken TV sets seen everywhere. In "Ocean of Fear" the viewer can see a wrecked tank and aircraft carrier, as well as the remains of a city on the ocean floor, even though there are Shrimp seen swimming about. The cause may have had to do with radiation, as sometimes, mutated animals may be seen. The River of Junk and the ruins around it are probably other remains of a destroyed civilization. In the episode, "It Came from the Nightosphere", a location called Red Rock Pass was littered with old battle wreckage. It is also possible that Finn may be the sole human being left in Ooo, besides Fiona, as stated in the episode "Her Parents " when Lady Rainicorn's parents say they thought that humans were extinct, though this may be just a guess or only evident in the Crystal Dimension. Even the Earth itself has been shown to have a massive amount of damage: "The Real You" reveals that the Earth has a massive crater that has wiped out a major portion of it's mass, making the world take the shape of a waning moon.

So far the nature of the disaster has not been revealed, and none of the characters have been shown to know about it or wonder how their surreal world originated. However, Marceline has been confirmed by Pen Ward to have been alive and human before the apocalypse. She somehow became a vampire before this all happened, allowing her to live through the entire event. Pendleton Ward stated that the apocalypse possibly involved a Mushroom War which will be talked about in season two. It is tough to state how many humans still exist in this world, considering that Lady Rainicorn's parents revealed when meeting Finn that they believed humans were already extinct before meeting him.