If you're outside the "walls," that just means you're on one of the exterior columns or rows. But you should still be able to move.
if you go to your Travel window, you should see the city. There should be an opening to the city, and to the buildings inside.
Neimoidia is a Trade Federation city, so I suggest you send a Darkness Mail (DM) to Jasko Faren. Tell him Belloq sent you. He should not only be able to tell exactly where you are, but should (I hope) have a ship to assign you for your travel.
As far as I can see there are no gaps in the wall here. The city facilities are completely enclosed by the wall around it. I exited the spaceport and ended up over the wall beside it. There are other characters here, perhaps stuck also (assuming I am indeed stuck).
I apologize for your trouble and I've forwarded your information up the chain of command. I don't have sufficient privs to view the city layout from my inventory screen and I'm in the middle of a several day hyper trip or I would come and get you myself. I've suggested that we send one of our members to come and land at the same coordinates that you're at so you can board their ship - please send me your exact coordinates which will be visible in the upper left corner of the travel screen. Hopefully that will be able to get you off the wall and on your way. I do not have an ETA yet and will reply to you via personal message.