I agree with glamourweaver. The poles are all at the same distance, but it's far more dangerous to travel towards those of Fire and Air, so the maps just show less of the north and south. You'll notice that the poles themselves are not visible on the maps. The idea that the poles actually move with the seasons is also neat!

Of course, nothing wrong with wanting an elemental imbalance to be there - I just don't have an idea for that