The world isn't flat, it's square

I spent most of the afternoon today testing the limits of Unity's new terrain system. Partly I'm learning how to use it, but mostly I'm trying to decide how to set up my game world.

Most terrain systems (Unity's included) work best with square terrains created from a heightmap (essentially a grayscale image whose pixels determine how high each point on the terrain mesh should be). The trouble with square terrains is, as you might guess, that the world is not square. You cannot fall off the edge. Unity terrains seem fairly flexible in that they don't have to be exactly square, and they can be adjusted to be quite large. Any really large terrain, however, would come with serious performance hits, since all its heightmap information would have to be stored in memory at the same time.

Because of this problem, most world-based games have chosen to divide things into sections and make the player look at realism-killing load screens when moving from one zone to the next. The notable exception is World of Warcraft, for which the good folks at Blizzard developed some way of streaming terrain information to minimize the number of load screens (this is one of WoW's most important innovations, in my opinion, because it allows a more enduring sense of immersion, and air travel).

So what are my options for piecing together a coherent world? Load screens are a necessity, I'm afraid, since Unity can currently handle only one active terrain at a time. Nevertheless, I would like to divide my world into squares that actually fit together. I may end up scrapping the idea, but I'm hoping that by planning ahead, I will be able to devise a way of making the game world feel coherent with some tricky, on-the-fly switching of higher- and lower-detail terrains. We'll see.

In the meantime, I have to work in squares. I take heart, though, that this is a time-honored gaming tradition. Think of the original Final Fantasy, where sailing your ship westward past the Earth Cave will spit you out on the eastern edge of the map near Crescent Lake. Sailing north will transport you to the world's southern reaches, where you will continue sailing north. It feels perfectly natural at first, until you realize that in a real, round world like ours, one cannot sail north forever.