I've been reading the blender reference manual and stopped at this:
Unlink Selection; Alt-L
Cuts apart the selected UVs from the map. Only those UVs which belong to fully selected faces remain selected following this command. As the name implies, this is particularly useful to unlink faces and move them elsewhere. The hotkey is analogous to the mesh Separate command.
I tried selecting pieces of my 'map' and pressing the hotkey, but nothing happend. I ask for a brief explanation of what is this and how it works. Thank you for your time.