Quote Originally Posted by Mholito View Post
I have a feeling it can unlock from any of the rank 50 sectors.
I believe this is probably the case.
I'm sure the undiscovered sector 23 is Diadem, and sectors 21 and 22 are closest in proximity to it, so that makes sense.
As per the below image though, it would seem even more likely that 17 would discover it rather than sector 20, which is further away.
Also because of it's greater distance, sector 19 would seem unlikely to discover it, but possibly for the sake of having all level 50 sectors able to discover the area, they may have included it also.

With any luck, some people will be able to post evidence of the remaining 2 level 50 sectors unlocking the zone.




On a side note, it would reasonably make sense that sector 16 would be in the area to discover the Diadem, however being under the required airship level to actually visit the zone, it seems less likely that it would be discoverable.