Joseph D. Farrell know what to add wrote in message . ..
Hello - I have been looking in the AIM and a few other places and am
trying to track down where enroute approach control end and Center
control altitudes begin.

Joseph,

I asked basically the same question sometime back, and the bottom
line seemed to be I'd have better luck asking for the moon.

Typically, the airspace controlled by a small TRACON may go up
to 8k or so; a major class B may go up to 14,000 ft or at least
require coordination until that height.

As for what altitude is best for you to go through an approach
airspace, that's going to vary depending upon your route and
the approach airspace in question, and even the winds and the
time of day. I would say, file for what you want and be prepared
to negotiate. Sometimes you can get through if conditions allow
you to request the IFR clearance VFR-on-top. Some TRACONs
are able and willing to let IFR flights fly through their turf.
Others operate on what we call the "GOMAB" principle (Get Out
of My Airspace Bugsmasher!) and will give you the wide-around.

You gotta understand that when you're IFR, to ATC you're a
slow-moving roadblock 5 miles wide and 2000 ft tall (I know,
I know, either 5 miles OR 1000 ft but the point is, they gotta
think about that swath of airspace surrounding you). So
depending upon how your exact route interacts with their
approach and departure patterns will govern what they can do.
If your flight path is perpendicular to their arrival and
departure stream, right over the airport at 4-6k might work
OK. If you're in a different place 4-6k might be impossible.

Dunno if this helps at all,
Sydney