There's about 16 unique tiles done so far, and I might just be lazy and flip the right hand cliffs to make the left hand cliffs (maybe with a bit of touch up so they look slightly different).
Next up is upgrading the map editor's scripting system to cope with layers and changing the Rescue Squad export script accordingly. I'm still not sure how they'll be handled in game, perhaps just as a generic landscape sprite with a drawing priority, perhaps something more specific (like distinct layers for terrain/buildings/decals/etc.).