Also avoid creating trees and other overhead objects. You see in a VTT app, the map we're creating is for the ground level. Once loaded the user then places PC/NPC/Monster tokens, specific objects. A layer above this is used to place trees and roofs, etc. Thus the tokens can be found between the overhead tree layer and the ground layer.

If you place a tree in your map, then VTT users will find their PC tokens walking on top of the tree, since it is on the ground plane.

Don't place trees, etc.