Ken S. said: It could be a drawing on the GM or Map layer, which changes the distance calculation for that square/hex, which would work for both ruler and token movement, and make the terrain obvious to the GM (if put on GM layer) or all (if put on Map layer). You can do that now,. It would be nice if there were pattern fill options (lines, cross-hatch, etc.) instead of just solid or none , but the basics are there now. Implementing an automatic calculation would also require a way to exempt those not affected (flying or incorporeal creatures in Pathfinder or D&D, for example).