What is high elevation?

[Prahlad]

This has been a recurring topic from both the 2007 and the 2010 symposium, so I thought I'd pose the question here: how would you define "high elevation"?

Is it simply based on altitude? For instance, any vineyard above 1000 feet is a high elevation vineyard?  If so,what do you consider the cutoff altitude?  There seems to be a lot of different ideas even about that.

Or does it have more to do with relative elevation?  So a vineyard at five or six hundred feet on a slope above a valley that's roughly at sea level could be high elevation, but a vineyard on a valley floor further inland doesn't really count even if the valley is 1500 feet above sea level.  What if the valley is 5000 feet above sea level?

Just to confuse matters, the European group CERVIM chooses to focus instead on "mountain viticulture" which they define in terms of slope and difficulty of access, so even vineyards on rocky, inaccessible shorelines or islands in the Mediterranean only a few meters above sea level can fit their definition of heroic viticulture.

So what do you think?  Are there enough shared factors or challenges common to all vineyards above a certain elevation regardless of how they sit relative to the nearby terrain?