So that no one else has to waste an hour trying to figure this out (because there is no documentation on this), it seems to be using lat and long values to center.
In my case, I wanted to center the map over the United States, which is LAT. 39°50' LONG. -98°35'. So I put 39,-98 in the center_condition expression.
Using zoom level 4, I got what I wanted.
