Changing map size?

Is there any way to change the size of a map without destroying the terrain? Maybe some way to copy the terrain and paste it in a larger map? Any help would be appriciated.

Yes you can copy terrain.

Make sure you're in terrain editing mode, then hit spacebar (I think) and drag the green box over your map. Then hit Edit > Copy. Then make a new map, and paste in in. Put it in the spot you want a voila.