The blank appears to be some kind of "combine 2 things" feature. Or something? I was messing around with it and it placed a route I'd just added directly over a river I'd just added. I'm not sure if it's just supposed to be used as a laying down routes on top of other features thing or whatever. Or if it can be used with other things too? I'll have to play around with it some more...
And yeah, the route thing has always been there. I think I've only seen it used correctly once. IIRC there was an early version of @DrGoNzO1489's Rox Valley that had routes layed down to show you exactly where the trails were. You could only see them by checking the nav map. I remember thinking "that's pretty cool, I wonder how he did that". I also remember seeing different colors for different trails. Which was even cooler. Hopefully he'll chime in here and give us some clues. Or tell me I'm delusional, and that never happened...