There are other clues. I was instructed to bomb the railyard at Athies Junction. Neither yard is very close to Athiers, but one is clearly closer than the other.

This is the briefing map zoomed to maximum on the same area. You can compare the roads, but the lines are not visible. I believe you would have to be very unlucky not to get the right one. Most yards are further apart than these two. The junctions have geographical place names and you can get a pretty good fix on them before you get into the air.