This window displays the entire contents of the active circuit. The circuit window itself is represented by the map rectangle and circuit components are drawn as black dots. When you press and hold down the left mouse button in the map rectangle, you can move it around in the map window. When you the mouse button, the circuit window displays the part of the circuit defined by the new rectangle size and position, and the circuit window scroll bars are repositioned to reflect the updated circuit view.
If any circuit objects are currently selected when you reposition the map rectangle, selected objects will also be moved, and their relative position retained in the new window. This functionality can be used to quickly move a collection of objects a relatively large distance.
The map window is a stay-on-top window, meaning that it will always be displayed on top of all other windows. You can show or hide the map selecting the Map Window option in the window menu, or by pressing the Ctrl+M key combination (quickly show it when it's needed or hide it when it conceals vital circuit window information).