PNP FF Ground Plane, GND or -9v?

[TySN_Sound]

I think I'm overthinking this and just confusing myself.

I have a bunch of GE trannies that will work for darlington pair FF's and I'm working on a PCB with the option of using a battery or adding a daughter board to convert DC jack 9v to -9v.
Either way, the main board will only ever have two power rails (Gnd and -9v).
I'm use to using ground planes on my usual positive power circuits, but with the negative supply, would I make the plane Gnd (the higher voltage) or -9v (the lower voltage)?

Within the circuit I want to say -9v, since the usual plane is the lower power rail (in effect pedals at least).
But I've always thought the plane should be grounded in respect to the whole system (i.e. the guitar rig ground, or jack sleeve) which I would think would be GND in this case.
Honestly don't know why I've thought this, or if it's correct.

Any help would be appreciated!
Thanks!

[duck_arse]

think of ground as common, instead, and your problem may go away.