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.
Working with the display windows
Opening a window
To open a window, click Windows on the main menu and select the type of display window you want to open.
The Magnifier Window
The Magnifier window works like a magnifying glass: as you pass the window over the data, you see a magnified view of the location under the window.
The Magnifier window allows you to see a magnified view of a small area without changing the extent of your data view. You can adjust the magnification by clicking the Percentage drop-down arrow or typing a value.
The Viewer Window
A Viewer window behaves like an independent view onto the map, and you can use any of the ArcMap interactive tools inside the window. For example, you can zoom and pan to a different part of the map to compare it with what is shown in the main ArcMap window. You can also identify and select features, perform editing, and so on. When you right-click the window, you'll get a menu of useful shortcuts. You can also use the toolbar at the top of the window to navigate your map. The scale for the Viewer window can be specified by clicking the Scale drop-down or typing a value.
A Viewer window can be used to work with inactive data frames side by side with the active data frame shown in the main ArcMap window. For example:
- For using multiple views such as those that are created using the ArcGIS Schematics extension
- For performing analysis and want to compare different results
Working with the Magnifier and Viewer windows
You can resize and set properties for both the Magnifier and Viewer windows. Click the right-arrow to open a shortcut menu for either window. 
You can use this menu to switch a map window between a Magnifier window and Viewer window. You can use it to set properties and synchronize the Viewer window's display with the location and spatial extent shown in the main ArcMap window.
You can also right-click in the display window to access additional display capabilities from the shortcut menu.
If you have dual monitors, you can put a Viewer window showing one data frame onto your second monitor to maximize your display area. Double-click the title bar to maximize the Viewer window. Note that the functionality provided in a Viewer window showing an inactive data frame is restricted. The main limitation is that you can't perform feature or graphic editing in the inactive data frame. When you hover the mouse pointer over a Viewer window showing an inactive data frame with a tool that is not supported, the pointer will change to show you that it is not supported.
The Overview window
The Overview window uses a box to show the extent of your display view within the total extent of your data. You can use the Overview window to navigate the map in the Data view display.
Using the Overview window to pan and zoom your map display
The Overview window displays a box showing the current extent of the map in your data frame. You can click and drag this box to pan and zoom your data frame display. To zoom in and out on your map display, click the corners to shrink and expand the extent of the box.
Setting other properties
You can set options for an Overview window by right-clicking the title bar and clicking Properties. For example, you can choose the extent's fill symbol and the window's background color. In addition, you can choose which layer is shown in the overview window.
It's often very useful to use an image or a basemap as your Overview window display layer. By default, the layer at the bottom of the ArcMap table of contents is the one drawn in the Overview window and is used to set the extent of the window.
Also, you can access the reference layer's Properties dialog box from the Overview Properties dialog box.