In aviation, a control area (CTA) is "a controlled airspace extending upwards from a specified limit above the earth", not less than 200m (700 feet), although the limit does not need to be established uniformly within a control area.
[1] Control areas are established in any areas when the density of air traffic is high:[2] A control area usually is situated on top of a control zone (CTR) and provides protection to aircraft climbing out from the airport by joining the low-level control zone to the nearest airways.
In the UK, they are generally class A, D or E. Control areas are particularly useful where there are busy airports located close together.
In this case, a single CTA will sit over all of the individual airports' CTRs.
In larger-scale cases, this is known as a terminal manoeuvring area (TMA, or TCA).