The flashlight and effects examples pretty much show what you need to know, but here is an example with a complete treasure map on one layer, and a blank map (just the second frame of the default map animation) and view hole sprite (with effect set to Destination out) on another layer which has Force own textures set to Yes.
Where ever you touch the map a view hole is created so that the player can see the completed portions of the map. There is a fade behavior on the view hole to make it fade in gradually just for kicks.
Of course if you want to expose certain locations on the map, you would carefully position the view hole rather than creating it where the player touches.
EDIT: I'm making a quick tutorial right now that goes into a little more detail about placing points of interest and exposing them through events. Should have it done by tomorrow.