Zone Transition?

[SupaCancerion]

Since the issue is really only present between Thanalan and Black Shroud, the easiest way I can think to address the issue (but not the best by any means) is to separate both areas by a huge mountain range that would occlude both regions from each other. Then the transition could simply be a tunnel through the mountain.

It's easier to imagine desert and rain forest on opposite sides on a mountain.

I would have to disagree with you and say that the problem is everywhere. The same thing happens when moving between Coerthas and Mor Dhona, Black Shroud to Coerthas, Thanalan to Mor Dhona, vice versa. The difference in scenery changes radically and abrubtly in each case.

However, the idea of a mountain range separating them is great. That's something that could very easily be done and would fix the problem quite nicely. I'm up for anything that would help make the transition seem more natural and realistic, and flesh out the world more.