Is Runeterra flat or round?

I noticed that the Freljord is actually to the west rather than the north or south. It confused me at first because we tend to expect the colder regions to be found up north and the hotter regions down south towards the equator.

I think it would be extremely interesting if Runeterra is flat actually because it means there is a completely foreign and different way climate would work and fits with the magical theme of the universe anyway.

Possibilities:

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Maybe it's round and sits on a different axis than Earth (the equator would run from north to south)

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Remember that it is a trade map for ships, that may be the best way for ships to reach the Freljord, it doesn't necessarily mean Freljord is directly to the west.