Terrain Math

I was wondering if anyone knew a good website or article that discusses creating terrain. However, I am not looking for a website or article that discusses the code, but rather one that talks about the math involved. So basically, I’m looking for a website that talks about the math behind creating terrain.

Here you go:
http://www.esite-host.com/~rocketmg/models/m_perlin.htm
http://www.vterrain.org/
http://www.geocities.com/Area51/6902/