In the vanilla version the east anglian region is depicted as being normal wooded land, whereas back in the time of the game it was all marsh and fenland and wasn't until the orange "revolution" that dutch landscapers managed to drain the land and put in place sea defences to protect the land. Then it managed to become cultivated. Also the British Islands were far more densely forested back in the time of the game, it was upon the norman invasion that alot of the wooded areas were cut down.

Just thought you might want to add this to your campaign map to keep it as real as possible. I know its only a small thing but I thought you might want to know.