In reply to:

This is clearly what the "edit original post" is designed for

zjemi, the lack of a tongue-in-cheek emoticon has been the subject of much discussion, and i regret that in rereading my previous post i can clearly see how you would interpret it as a slight to you, rather than a not-very-well executed show of levity.

FWIW, i *still don't think the intent of the "edit" capabilities is to substantially change the content of your post after it has been responded to, for the simple reason that many of us don't read the threads in real-time, and it can get confusing. perhaps an additional clarifying post in response to tsuwm's reply would've been helpful. also, most of us don't review the original post once several responses have been added, so additional information provided therein will most likely go unnoticed.

as to your initial query, it isn't hard to imagine that contour flying, because it is by definition conforming (and in close proximity) to the contours of the earth (caused by vegetation, obstacles, and even ambient light) could be called "nap of the earth" flying because the pilot is conforming to the "grain" or "nap" of the topography.

Has anyone checked the OED for a literary reference? You may be onto something, zjemi, only because i can't imagine a bunch o' big ol' macho army-types admitting to even *knowing* the word 'nap' (which i tend to think of as a sewing term), let alone applying it in this case.