Best zoom level for google map

It's an undocumented API call doing it. Here's how to use it:

var center = new GPoint( (maxLon+minLon)/2, (maxLat+minLat)/2 );
var delta = new GSize( maxLon-minLon, maxLat-minLat);

var minZoom = map.spec.getLowestZoomLevel(center, delta, map.viewSize);

map.centerAndZoom(center, minZoom);

That's it :)