To Warpstorm: you're right. And with two entire courses in projective geometry I should have known that... Anyway, that's a good point about they being essentially impassable up until the 20th century so forget that. I guess my main point is that I'd like the maps not to be rectangles.
What I'm thinking is having the possibility of round maps. The minimap would be an actual sphere (the planet), but empty in the middle so you could see the main face and the one behind. The main map would still be rectangular and would correspond to a projection of a rectangle on the sphere. You'd play normally on the main map but on the global scale, you would actually be playing on a planet. You could also rotate the sphere in the minimap to get a better view. With this you could have ice caps at the poles, icebergs and a very planet-like feeling. Anyway, I've drifted a little...
What I'm thinking is having the possibility of round maps. The minimap would be an actual sphere (the planet), but empty in the middle so you could see the main face and the one behind. The main map would still be rectangular and would correspond to a projection of a rectangle on the sphere. You'd play normally on the main map but on the global scale, you would actually be playing on a planet. You could also rotate the sphere in the minimap to get a better view. With this you could have ice caps at the poles, icebergs and a very planet-like feeling. Anyway, I've drifted a little...