"tony zambon" wrote in message
m...
[...] how do you
determine the lowest cruising altitude in conformance with the
hemispherical cruising altitude when the ground elevation is always
changing
by thousands of feet?

I'm not sure I understand the question. The rule applies only about 3000'
AGL. If terrain rises placing you below 3000' AGL, then the rule doesn't
matter. If the terrain drops placing you above 3000' AGL, then the rule is
the same as it is everywhere else.

Why would you ever need to "determine the lowest cruising altitude in
conformance with the hemispherical cruising altitude"? Or if you prefer,
what's so hard about doing so?

What you actually need to do is pick a cruising altitude that puts you at an
appropriate altitude above all obstacles, and then do your best to make it
conform the hemispheric rule (you may be limited by oxygen requirements or
climb performance, and this may be true even for the purpose of simply
clearing all obstacles).

Pete