I stumbled on to this method of hiding map sections for your players. I didn't like any of the options that I had seen or used (covering with paper, drawing as you go, etc.) so I tried cotton balls. Below pic is poor and I needed more cotton balls than my quick raid of my wife's supply could yield, but I think you get the idea. You can be very selective of where you remove them and it really has been working well so I though I'd share.