The world of Dragon Ball is depicted as a large globe. The globe is divided into two halves, or the upper and lower world, seperated by a large body of cloud with Lord Enma's Palace in the middle. The Lower World is what is called the 'Universe' and also inhabits Hell, while the Upper World is called the 'Cosmos' and inhabits Heaven.
Beneath the clouds lies Hell, a place were disembodied spirits go to reside once they have passed away. They are judged prior to this by Enma however. If they are judged to have committed too many atrocities, their souls will be cleansed and recycled. If they have a number of meritorious achievments under their belt, then they ascend to the Upper World and usually have their physical bodies restored. The rest however, reside in Hell. Not much is known about Hell aside from it being a dark, wasteland type place and there is allegedly no way out, if you fall through the cloud barrier.
Beneath Hell in an enclosed 'space' exists the living realm, where the main settings of Dragon Ball can be located. It's divided into four galaxies, Northern Worlds, Western Worlds, Southern Worlds and Eastern Worlds. Earth, Namek, Vegeta and so on are/were all found here.
Above the clouds exists Lord Enma's Palace where spirits of the dead are judged. The Serpent Scale Road connects this place to Kaio Sama's Planet which floats above the tip of it's tail, or used to before it was destroyed by Cell. There are three other miniature planets here as well, presumably residing the other lords of worlds. These planets have yet to be shown, however.
- Dragon Ball Landmark, page