Terrain association is basically reading a map and not using a compass. If I am standing on this hilltop and there is a stream over here and a saddle to my right I am right here and I need to go this way. Its hard for me to explain. Being a tanker I have almost never used a compass when navigating. Being in a big steel box it isn't very easy to get a good reading with one. LOL. Also I'm normally traveling faster than 25MPH. I have learned the ability to glance at a map and be able to travel extended distances by just reading the different types of terreain that is around me. Following depressions or ridgelines. I guess that after years of coordinating crew duties, navigating my tank, and communicating on the radio, all at the same time, it is just a natural thing to me.

There is a pretty good explanation of terrain association at: http://www.globalsecurity.org/military/library/policy/army/fm/3-25-26/ch11.htm

(sorry, don't know how to post a link here.)

Global security is a great resourse to find information on the military. Check out all of the nice unclassified FMs available to you there.