I want to make an island far far away...

Another question, is exterior landscape really infinite as bethesta says?

:-)

First, yes, you can create an island in an interior cell. Mournhold is done this way, with a huge wall to keep you from noticing. What you can't do is landscape the way you do true exteriors - because there is no landscape. You have to put in *ALL* of the landscape meshes yourself, and unless you find a clever way to deal with the edges, a player who swims far enough will see the edge. There are different ways to handle this, including a script that jerks the player back to shore if they swim too far out, or just putting invisible barriers in a perimeter.

There is a nifty tool that will let you prototype your island in exterior space, and then export it to a mesh. http://yacoby.silgrad.com/MW/Mods/dlmeshconvert.htm I haven't used it, but I'm told it's quite effective.

Second, yes the exterior landscape really is infinite, for small values of infinite. However, there is a strange bug that causes the viewport to oscillate/vibrate/act weird the further you get from 0,0 (the origin) It's not really a problem unless you are *REALLY* far away, though. I'm doing a mod that places a landmass with a northernmost point of 55, and I haven't noticed the shaking out there. I'm not really sure if this 'bug' affects all systems, or where it begins, as I've only run across it once while messing with really long jumps.