In Daizenshuu 4, Daizenshuu 7, 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 realm of the living (or "The Universe") and the Other World (or "The Cosmos"), with Hell located between the two halves.
The realm of living is divided into four Quadrants, 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 located on the four sides 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.
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 Demon Realm, where the Makaioshins (the complete opposite of the Kaioshins) live, is located on the very bottom pin/tip shaped of the universe.