The overview map displays the full or partial extent of a layer with a red box outlining the current extent of the map. A full or partial extent is displayed depending on how far you have zoomed in.
Click the View menu and check Overview Map to add an overview map panel.
Right-click on a layer listed in the legend and click Use in Overview Map.
To remove the layer, right-click the layer listed in the legend and uncheck Use in Overview Map.