Map object computes the mapping coordinate projection from the given parameter. The object is compatible with all material mapping objects which use a 3D geometry to define the mapping function. Surface defined coordinates (vertex variable interpolation etc.) are not supported.
One important use of the Map object is to provide a consistent parametrization for randomized sampling. For example, a volumetric fog shader may change the sampling position sligthly to examine the surrounding volume better:
volume properties vector variable pos vector variable mc vector variable delta delta = random(map coords) pos = add(coordinates, delta) mc = Map(pos) turbidity = Noise(mc) ...
This kind of fog density definition appears consistent for a moving camera, self-shadowing fog etc.