To understand how this works, imagine the way that an object would float if it was tossed into a gigantic pool of water. The surface of the water would then show the exact location of the gravity plane in relation to the object. The positive field pulls things toward the surface of the gravity plane. The negative field pushes things away from the gravity plane. Because space is three-dimensional, the gravity planes of different world could be oriented in different directions and might even be mobile, changing as the worlds themselves rotate or revolve.
Neutral gravity has no equivalent with common laws of physics affecting other game worlds.
This allows the existence of exotic flat worlds, but they need to be slightly concave or have walls or mountains around their edges in order to retain atmospheres. Some disk worlds rotate as they revolve around their suns, giving them day and night cycles, but some face always toward or away from their suns. Some also spin like records, producing spiral cloud patterns and winds of up to hurricane strength. Flat worlds are loved by cartographers because they are so easy to map. These strange planetoids are often found among asteroid clusters containing debris from the original world.