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?

Why do you care if you're talking to approach or center?

-Robert, CFII