Yeah. It's random, but it's logical. I assume it first creates a general design for the world, then gives it random caves, adds water and rivers, adds lava under and above ground, adds minerals in correct locations. It does do weird things like create floating islands occasionally for some reason. While that's cool I hope it is fixed for more realism. I started a world once and just as it loaded, a whole shitload of gravel blocks fell from the sky like rain because they had spawned in the air but gravel blocks don't stick to walls so they fall as soon as their supports are removed. Sand works similarly but will stick until a connected block is removed.