In the feature-separation approach, the major features to be printed in each color are divided into groups before they are combined to form a master color plate for printing, making it possible for a map user to prepare maps and omit extraneous information. Some features are printed in more than one color. You can order film materials of any available feature separate or a composite of two or more feature separates. The thicker film is also a good stable base material for uses requiring accurate registration of separates or composites and is the preferred material for most applications. Left reading or right reading is based on viewing the film material with emulsion toward the reader.
Right reading means that the image is readable from left to right.
Since the emulsion contacts the reproduction medium, it avoids any distortion caused by exposing through the thickness of the film. It is also used for stick-up materials, such as names and symbols on transparent tape. In many cases, map separation materials can be requested without the open window separation. The standard screen used by the USGS is 50 percent. Some map separate materials may not be available.