Masks can be either solid black and white or they can be grayscale.
In Photoshop, the white area of a mask is the area which will be selected, although there is always an option to inverse the selection. Using masks you can create a wide range of effects such as shadows and vignetted edges, apply maps to any bitmapped image such as a photograph to create a montage, and most importantly, use the masks with Mountain High Maps relief images to create dramatic, highly effective, and professional maps. These correspond with the city names in the FreeHand and Illustrator files. Cloud mask for the world maps 6.04 and 6.05. Although the masks really come into their own when used with Photoshop's Alpha Channels, you can also use the masks to apply quick and easy selections to a map without using channel operations.