Unlike sheep, pigs don't have a clear leader when they move around. They'll all look up, and then take a couple of steps, and the migration begins.
When they're small I keep them on a fairly loose leash. I have a good perimeter fence, and the pigs tend to wander 5 or 6 acres in an L shaped pattern. They're very much creatures of habit. I can't quite set my watch by them, but I pretty much know where they'll be at any point. And they stay so close to each other that if I find one pig I'll usually find all of the other pigs within 20 feet.