I think the 'Outer Area' is a mode C veil around the class C (or B) airspace. In the US there are a handful (~10) of Class B airspace areas, and about 30 odd class C airspace zones, the rest is *gasp* D and E.
Above class C, you mostly have *gasp* class E (with NO transponder requirement).
I will verify on my copy of the AIM and charts when I get home next.
Bevan..