Mxsmanic wrote:
What determines the boundaries between airspace managed by an en-route
ATC center and an approach or departure center? I don't see any clear
indication of which is which on sectionals. There are boxes saying
who to contact for approach, but nothing that shows where the handoffs
between terminal control and center usually occur. Is there a general
rule?

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I'm sure you'd be able to find out the answer to this question by being
in aircraft for 10 hours. Get together with an instrument instructor
and do about 10 flight hours doing departures/enroute/arrivals. Note
down on your sectional where the handoff occurred. That would be the
best way for you to learn the reality of your question. Since of course
you are paying this instrument instructor (and of course renting the
aircraft) I'm sure the quality (and relevance) of the answers will be
much higher. I'd suggest a G1000 C182.