I would agree on Green Knight's maps for Cerilia (and population). I've always considered Cerilia to be about the size of Europe. Think of the various terrains, climates, etc. that exist there.
When I read that Cerilia was the size of Western Europe, I was shocked. I figured it was done by the same guys who tell a woman:"No, that's 6 inches, really!"

And the topic is titled How big is Cerilia in miles, yet half of the topic is spent on how many miles could an army traverse or carry. But I think it's an important issue. I've seen a campaign fall apart because of a disagreement on that part.

Yet another issue that arises if you make Cerilia as big as Europe is the population. And I prefer larger figures, they make more sense.