Hmm, ok so I'm beginning to see what you mean. It's something similar to if you specify a resolution bigger then your monitor in Linux (something you have to do sometimes to get around limitations when using dual monitors) combined with the idea of virtual desktops but instead of having to switch between each of them (well you still are, but now it's just panning around instead of switching between them with a keypress).
You can have a virtual screen (desktop), which is screen area that is larger than the physical screen and which is panned by moving the mouse to the edge of the screen. If you don't want virtual desktop at a certain resolution, you cannot have modes listed that are larger. Each color depth can have a differently-sized virtual screen Please answer the following question with either 'y' or 'n'. Do you want a virtual screen that is larger than the physical screen?