Where is the center of an infinite plane?

I ask that because I have a game setting- or a novel setting, or SOMETHING. It's a place where there IS a center on this flat, infinite plane. The infinite world is divided into four infinite planes, EACH sharing two FINITE planes with its twins. The world runs INFINITELY in each of the 4 directions- NW, NE, SW, SE. Along N, E, S, W, at the center- that's there the splits are.

Each plane has 2 edges that it shares and thus has an end IN that direction- but never stops otherwise.

2 of the four planes extend INFINITELY upwards- one has nothing but space, the other- well, it's weird with pillars and surfaces :) The other go extend infinitely DOWNARD- one is nothing but OCEAN forever. The other is divided up- is it INFINITE OCEAN with bubbles of island, or is it infinite land with bubbles of ocean?

And the people, of course. VERY different to get used to at first. After all, there IS no sun- there is just the Glow. And people NEED the Glow- cover your body it HURTS where the glow is blocked. Get cut? The blood dries into... mud. A corpse, unless treated, will dry into- dirt.

It's a fun place, K'yenwald :)