[@Monochromatic Rainbow] Well, here's a renegade thought of mine.

We all simply assume, because Westeros fills all the maps we see, that it's gigantic. However, we also see another continent in the southwest, Sothoryos. It's a tiny corner, but it implies that the continent must be quite a few levels larger than the two we can see. There is the possibility that Westeros is smaller than advertised. Maybe it is in fact about the size of Britain or even smaller for all we know.