Tomb of Annihalation map reading confusion- Fane of the Night Serpent

Scattered across the map of the Fane of the Night serpent are these +x ft.  markers on the GM layer.  I noticed them on the official map in the book version too but can't seem to find any reference to them.   Can anyone tell me what these are?  I am finding it very confusing and I fear it's an important detail I won't be able to convey to my players.

Height?

Dick K. said: Height? I wish I knew.

Fairly certain that’s the height of those areas above the floor of the main room...I can’t point to anything specifically but I’ve seen similar notations in other adventures....

Definitely height (in feet) above the surrounding area, to denote ledges, balconies, etc.

In hindsight, that makes a lot of sense.  Thank you for the insight guys.  There's still some weirdneses left on other parts of the map but I think this explanation makes the most sense.