Unlike most examples of this trope, the anti-gravity actually does play a crucial plot-point: Robotnik's end-goal is to destroy the northern pole, which anchors the Land of the Sky to the Land of Darkness, whereupon the continents' anti-gravity properties will see them be hurled into space, killing everyone. This "inner world", called the Land of Darkness, is completely uninhabited except for Robotnik and his Mecha-Mooks, so from the perspective of the inhabiants of the Land of the Sky, they live in this.
Sonic the Hedgehog: The Movie: Planet Freedom consists of a series of floating continents above an otherwise normal planet.There is downward gravity: people can fall off airships into unknown depths.
Universities send explorers and cloud biologists on expeditions into "uncharted air". Airmen in steam-driven iron dirigibles trawl the aerial trading routes between city-states. The Mysterious Geographic Explorations of Jasper Morello is set in a gothic- Steampunk world of floating islands and floating Victorian-style cities wreathed in smoke and criss-crossed by bridges.Other times, it may be in Another Dimension or an Elemental Plane where things don't work quite by the rules of regular physics. In some cases, the World in the Sky may have been created or settled specifically to escape whatever made the original surface unsuitable for life. Sometimes, a World in the Sky may be placed above a more conventional world which, for whichever reason, is largely or entirely uninhabitable. Sci-fi versions will generally be landmass floating inside gas giant's atmosphere.
Do not expect the outcome of falling off the side of one of these pieces to be properly explored. What keeps them hovering? Where does the gravity come from? What's keeping the atmosphere in place? What, if anything, is there at the "bottom" of these worlds? Nobody knows, but maybe A Wizard Did It. Impossible note or nearly impossible - see The Integral Trees under physics resembling ours, worlds of this type are usually found exclusively in fantasy. They can range in size from tiny "islands" to huge continents with vast civilizations. Landmasses, with or without internal seas, float suspended in an atmosphere. This is less a World Shape, and more a series of world pieces.