Linking maps to each other

How can I link maps to each other like in Frozen Throne's orc bonus campaign? Or is it even possible with the editor? I would appreaciate any help.

This is made by Campaign Editor (in World Editor), F5 probably.

So that when I go to a certain point of the map (like circle of power, or a portal) I will move to a smaller map?

It is not possible to link maps in multiplayer ways.
In single player, their is a action to set the next map played = (filename).
The filename must exsist, and to enter the map you must have victory (as far as i know).

But yes, it is also do-able in Campaign Editor