The other day I was looking over some ISO dungeon maps and thinking "these are pretty, but how are they even useful".... and now I see how A secondary picture is pretty much the way to go to set the tone (I play VTT so I use tone images all the time to get the idea across of a setting before loading up maps). to try and do this with JUST the map is going to be harder than that, but not impossible.

Some ideas on how to demonstrate it:

- Experimenting with the shadow. If you made the map a sunset/sunrise picture so that the light source is coming from a side on position as oppose to directly above, you can show that the shadow isn't connected to the rock at its base giving the effect that it is floating. With some long shadows from things actually on top of the landmass (rocks/trees/buildings, etc.) it will show that you do actually know that shadows should be connected, so obviously the big shadow has been disconnected for a reason!
- Have something running from one side of the landmass and underneath it, like a road or a river (something that wouldn't/shouldn't have any breaks in it). It's doing to difficult to demonstrate that the road or river goes under the landmass as opposed to around its base but might work as an added element to show the the terrain under the landmass is passable.
- Use some semi isometric perspective techniques (see BigBlueFrog's current Lite Mapping Challenge from this month) then you may be able to play with the image and give the right impression.