For lack of anything intelligent to say, the Old Quibblemeister says terrain can't
really undulate. Waves are essentially sinusoidal, with rounded crests and troughs
and even spacing of crests. Terrain has sharp peaks, flat surfaces, and just about
never even spacing of crests. Smug evil grin.

As a bit of trivia, I believe I know origin of the admonition "Don't make waves." In 1936
I was in the college infirmary, which was in small community hospital. A black man in
bed next to me told me a joke about a black man going to Hell, and being given a
choice of rooms in which to suffer his punishment. He chose one in which transgressors
were floating in very vile liquid excrement. When he tentatively dipped one toe in it,
a distant voice boomed out: "Careful, n-word, we don't want no waves in here!"