This example shows how to work with the OverviewMap component. It inherits
from Ext.Component wrapping the OpenLayers Overview control. This means
you can place it in your applications layout as you would any other component.
The example shows the usage of an GeoExt.OverviewMap as an item of a
Ext.panel.Panel inside a vbox layout. The overviews map size is ultimately
determined by the parents dimensions.
The OverviewMap component has not been configured with a map so it defaults to the GeoExt.panel.Map guessed at runtime.
The js is not minified so it is readable. See overview-generic.js.