I know this has already been suggested and it doesn’t seemed to have gained much support, but I can’t see why.
When you’re dealing with thousands of passengers and baggage and tens/hundreds of planes and vehicles, it would be immensely useful to have planning tools. When I end up building too big or too small for a check-in area, shops etc. I always think it could have been averted if I could have drawn out my plans in the game (instead of visualizing the squares or using paint or something).
I would propose a simple Prison Architect sort of solution - different shading for paths walls floors roads etc., and the addition of free-placed labels too (like “terminal expansion here” or whatever you’re planning). Many minutes and even hours, as well as my sanity, could be saved with such tools