Bertin: Semiology of Graphics geometric primitives: marks points, lines, areas, volumes attributes: visual/retinal variables parameters control mark appearance separable channels flowing from retina to brain [x,y] position [z] size, shape, greyscale, color, texture, orientation data types nominal, ordinal, quant [Bertin, Semiology of Graphics, 1967 Gauthier-Villars, 1998 EHESS] 73