I had a time with this as well. What I found was that the "13" is overridden by the code following it;
var bds = new GLatLngBounds(new GLatLng(20.8258173, 3.74226154),
new GLatLng(23.2391067, 6.92817646));
The map can be zoomed by changing the red sectons. It takes some work with a map and a calculator to find the correct lat/long figures for the location you want to view.
I found the google information helpful as well here - http://code.google.com/apis/maps/documentation/reference.html#GLatLngBounds.GLatLngBounds
you can view the map I got to work here - http://www.simpilotgroup.com/newenglandair