Perhaps space is not indexed - but our system of GPS satellites would seem magical to ancient sailors. We could speculate that if a civilisation has solved some

Perhaps space is not indexed - but our system of GPS satellites would seem magical to ancient sailors. We could speculate that if a civilisation has solved some of the problems of interstellar and possibly FTL travel, they may have an analogous system, subspace location beacons (to use Star Trek buzzwords). With a system like that, marking out a piece of 3D space would be simple enough, like avoiding landing your plane on an island where the natives were less technologically advanced and hostile.