As things stand, Scottish ski terrain is divided between conventional piste classification (black/red/blue etc) and off-piste. Now there's a proposal to re-designate the main 'back corrie' at Nevis Range - Coire Dubh - as an 'itinerary' (unmarked, unpatrolled). It's proving controversial.
Story by Roger Cox in the Scotsman:
Debate on Winterhighland:
Nevis Range existing map: