All maps end somewhere. if you take the fakeconsole and run in one direction all the time you will find the end. Like CressAlbane said the moders hide them by objects, hills or fog.
For the edge of the field, all the maps i saw, I feel there is something that hides the edges of the field, even when you are at a certain height. there as a background image.
Many maps have objects that block of the player from reaching the edge, like the mountains and canyons on geonosis. There are also map boundaries which kill a player if they go to far. You know, those "Warning. Return to battlefield" things. I'm on a tablet right now, so I can't give you a link to more info at the moment.
@grievous:
Anakin is right, it's impossible to completly hide the background. But if you place your CPs enough in the center of the map et you place high mountains props, the problem will be fixed
Hidden/Spoiler:
Anakin a raison, il est impossible de cacher entièrement le fond. Mais si tu places tes PCs suffisamment au centre de la map et que tu places des props de montagnes assez hauts, le problème sera réglé