Area 1: Americas, Hawaii etc.
Area 2: Europe, Middle East, Africa, etc.
Area 3: Japan, Asia, SW Pacific, etc.
Going from Area 1 to:
Area 1 you can't transit in Areas 2 or 3
Area 2 you can't transit in Area 3
Area 3 you can't transit in Area 2
Going from Area 2 to:
Area 1 you can't transit in Area 3
Area 2 you can't transit in Areas 1 or 3
Area 3 you can't transit in Area 1
Going from Area 3 to:
Area 1 you can't transit in Area 2
Area 2 you can't transit in Area 1
Area 3 you can't transit in Areas 1 or 2