That's an excellent question. Thanks for bringing it up.
I don't know of any easy way to determine the lines of operation for any given map. This info needs to be in the "Mission" part of the F7 page if it's not available anywhere else.
Now, you *could* look around the edges of the map for some wagons, which I believe are always at the lines of operation, but the demo will lock up tight if you approach the area of the map where the French lines are.
The lines of operation for the Montebello map are the roads in the center of the map leading off map east and west. There are actually two for each side, but they're on top of each other so the effect is only one line of operations per side.
Hook