One analogy I have for how I understand what I mean when I say personality center is this...in our psyche there are a multitude of birthing points for complexes or personalities to originate. Perhaps there are as many such centers of origin/focus or personality centers as there are stars in the night sky. When those personality centers are coordinated then you get constellations aka complexes. The ego, the shadow, the anima/us and other characters may be collections of these constellations. Perhaps, the Self is the galaxy that all these stars revolve around.
An interesting extension of this analogy...if one has a different star/personality center than someone else then the stars will be arranged differently in your "night sky" and so when someone else points and says, "Hey those stars look like a ____", you might not see quite what they are seeing.