A generic term for a class of techniques that attempt to construct a low dimensional geometrical representation of a proximity matrix for a set of stimuli, with the aim of making any structure in the data as transparent as possible. The aim of all such techniques is to find a low dimensional space in which points in the space represent the stimuli, one point representing one stimulus, such that the distances between the points in the space match as well as possible in some sense the original dissimilarities or similarities.