Looking at this wonderful map over on Cartographers Choice: http://www.cartographersguild.com/ca...ia-daelin.html I have noticed that there are a few maps that do the land through the centre thing from top to bottom. I can't think of any that have the land running horizontally through the centre and water top and bottom. My suspicion is screen and paper orientation making it visually convenient to to it that way. i.e. side to side is usually wider.