This sample application shows how you can use a smaller map as a locator for the larger map.

To try this example out, click and draw a track zoom rectangle on the Map Locator.  This will automatically zoom to that extent on the larger map.  Any track shapes drawn on the large map will also be represented on the Map Locator to keep the displays in sync. 

This type of functionality becomes very important when a user zooms into to a very detailed area, but still wants to see where the current extent is located in reference to the entire map.