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Layers are also used for allowing users choices, e.g. between roads and railways on a map. |
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Layered models are sometimes called ''2 1/2-D computer graphics''. They make it possible to mimic traditional drafting and printing techniques based on film and paper, such as cutting and pasting; and allow the user to edit any layer without affecting the others. For these reasons, they are used in most [[graphical editors]]. Layered models also allow better [[anti-aliasing]] of complex drawings and a sound model for some popular modeling concepts such as [[mitered joints]] and the [[even-odd rule]].
Layers are also used for allowing users choices, e.g. between roads and railways on a map.
In a layer-based model, the target image is produced by "painting" or "pasting" each layer, in order of decreasing depth, on a virtual ''canvas'' -- a [[digital image]] initially colored with an uniform [[background color]]. Painting one color over another at a particular [[pixel]] results in the second color, or in a combination of the two colors if the layer includes some transparency.
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