An Overview map is a useful tool you can add to your map. It allows a user to see the extents of the map and makes it easier to pan around their data.
Adding an Overview map is a little tricky because the Overview can't be added until after the Map has been drawn. To do this, listen for the "afterDraw" event of the Theme Manager.
When this event has fired you can create a new OverviewMap control and add it to the map.
In this example we also maximize the control so it's visible by default.