The Military uses of the Palantiri.

[JeffF.]

I don't think that was as great a problem as you state, take Umbar Any gathering of the Corsair fleet or preparations for war would take place in that great harbor. If the Haradrim invaded they must use the river crossing of the river Poros. The great nations of the various Haradrim & Easterlings must have had large cities, at least capitlos, these also would be known and the centers of marshaling any great hosts. Finally Barad-dur was known and the passes out or Mordor. These would all be focal points for observation.