Universe 7

The Dragon Ball Universe (宇宙, uchū) is the totality of existence, including planets, stars, galaxies (銀河, ginga), the contents of intergalactic space, and all matter and energy. The Seventh Universe is where Earth II and the whole Dragon Ball series is set. The main hero of the series, Goku, uses his incredible strength and sense of good to combat the evils that plague all around this universe.

Contents and structure
In Daizenshuu 4, Daizenshuu 7, Dragon Ball Landmark, and the Dragon Ball: Super Exciting Guides, Akira Toriyama explains that he envisioned the Dragon Ball cosmos as a big ball. This ball is divided up in two halves: the lower half is the realm of the living (or "The Universe") and the upper half is the Other World (or "The Cosmos"), with Hell located between the two halves.

The planet of the Kaioshins, the top-tier deities of the universe who watch over both the Other World and the living world, is located outside of the ball, in the Sacred World of the Kais. The Kaioshins are Gods of Creation who provide the catalyst for life and planets to be born. In order to provide a balance to the constantly increasing number of planets, the Gods of Destruction regularly destroy life and planets. The Demon Realm, where the Makaioshins (the complete opposite of the Kaioshins) live, is located on the very bottom pin/tip shaped of the universe. The realm of living is divided into four quadrants based on the cardinal directions, each ruled by a Kai chosen among the Shin-jins from Planet Kaishin. There is one Check-In Station for the four Quadrants of the universe, which allows its inhabitants to go to the Other World. The Kais live in the Other World, on planets positioned at the four cardinal points of the cosmos; notably, North Kai's planet is at the end of a Snake Way which starts from the Check-In Station. The Grand Kai's planet is above Heaven, which is a gigantic planet in the center of the cosmos. There are roads leading to each Kaios' planet.

Places in the universe
The two Quadrants of the universe where the Dragon Ball series is set are the North Galaxy and the South Galaxy. The universe that the Earth II is part of holds a past where hundreds of planets have been destroyed through Majin Buu (creation of the dark mage Bibidi).

Trivia

 * Toriyama said that the structure of the cosmos was so that it would be easy for both him and the readers to understand.
 * Akira Toriyama himself is included in the character dictionary in Daizenshuu 7, being described as the ultimate ruler of the Dragon Ball universe and a gentleman far, far greater than even the Kaioshins.
 * In the video game Dragon Ball Z: Buu's Fury, Grand Kai's planet is located outside of the ball, below the Sacred World of the Kais.
 * The Seventh Universe is a parallel universe of our Universe.