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
To the planning tool i would add a copy too. I got used to test a layout but then i have to manually copy it everywhere. It would be easier to select an aera and then copy paste it elsewhere.