First of all, the spawn is just that, a spawning point and has nothing to do with landing a GV at all. In fact, it's often the worst point trying to end a GV sortie, as it's a very likely place for the enemy to look for you.
It all just depends on enemy proximity. I don't remember the exact value, but it is about 6k of distance. If there's no enemy player within that radius (including pilots on foot or in manned guns), you can 'land' your sortie successfully anywhere, even on enemy bases.
On your home turf, you can still land with enemy withing 6k, but you will get a ditch (if you are undamaged and not on concrete).