I don’t know if this is possible, but hear me out, we all know how frustrating is to wall on hills and end up having a hole, so I’m proposing the devs to make a “Walling mode” which, when you press a hotkey it will stop the hills from rendering, all the map becoming flat until you press it again.
You can even take this a step further and mark the boundaries of buildings, trees and cliffs more clearly on this mode, which would reduce the need for small trees or cube mods
As I said, I don’t know if this is feasible on the engine, but I think it would improve the game imo
Also in the topic of improve walling, I want to “bump” Age of Salamanders (Optimal Walling: JavaScript to test a QoL (Age of Salamanders)) It would be so useful and it doesn’t get the attention it deserves
Thank you for putting light on this topic and for the suggestion 
In fact, regarding the holes topic, the Age of Salamanders also shows an algorithm to improve this: the Tile Indicator, that you can test here (which would also require to press a specific hotkey, like your suggestion).
I much rather have the QoL suggestions of AoS, then this suggestion.
Idea is great ! I made visualization.
Building while holding hotkey.
Second example:
Hole in the wall
Holding a hotkey.
Great Visualization! thank you
Yes, I’m aware, I really liked most of your suggestions in AoS, but I think the Tile indicator is too complex and a bit of an overkill, my suggestion would be a little more “vanilla”, and would make less people angry like they did with Auto Scout
I remember in the old age, when using low graphs, the hills would be seen like terraces. IMO was easier to see the holes in that mode.