Re-masking/hiding areas of a map

[yeknom]

Let's say that a party is in a large area and they are exploring it over a long period of time and I wish to re-mask portions of the map they have already explored, how would I go about doing this without having to remove the entire mask and add it again before removing the sections of the map I want revealed? I am asking if there is a way to easily re-mask sections of the map once they have been revealed to the players and if so, how is this done?

[damned]

Easy :)

[Shift] + Mouse does irregular shapes of unmasking
[Ctrl] + Mouse does masking
[shift]+[Ctrl] + Mouse does irregular shapes of masking

[yeknom]

Thanks, it is much appreciated.