I’m getting ready to run Icewind Dale, and noticed some of the maps have this marking in them, but none of them call attention to it or explain it. Does it indicate height, or something weird like “this ramp is a right triangle with a hypotenuse of 30 feet” or “30 feet extra ramp here we didn’t have space for, stretch it out when you run it”?
The description of room K3 gives some clues; it describes the different bridges as “the 50-foot-high bridge” and “the 30-foot-high bridge”.