ArcMap provides three additional map windows to view the spatial data on your map: a Magnifier window, a Viewer window, and an Overview window. When you don't want to adjust your map display but want to see more detail, retain a particular view of an area, or get an overview of an area, open another window.
All these windows operate with Data view and not in the Layout view. You can also simultaneously open more than one of these windows.
In this tutorial you will learn how to work with Magnifier, Viewer and Overview windows.