From what I've understood, in Canada a Terminal Control Area (TCA) is established at airports with a high volume of traffic to provide IFR control service to arriving, departing and en route aircraft.
A Control Zone is designed around aerodromes to keep IFR aircraft within controlled airspace.
Why do we have both? Both provide ATC services, so why do we require a Control Zone within a TCA? Is there a specific reason that the TCA cannot be lowered below 700 AGL?
See this reference material in "From The Ground Up" (I've tried to attach it but it didn't work).