A second principle is that a single view can be displayed in multiple locations. A third is that all but the simplest views are hierarchical in that they contain subviews. The principal responsibility of such views is the layout of their subviews. Subviews of views can in turn have subviews and so on to arbitrary depth. Spatial layout is can also be used to demonstrate relations between two variables mediated by a third.
General layouts are themselves views and so can be subviews of other views.
In this way, arbitrary interfaces can be made. If such representations are to be successful the physical entity used to represent a number and the psychological sensation of size elicited by that entity should be proportional. This linear relationship does not always hold and it is interesting to examine the ways in which bias can be introduced. In some situations the pattern of errors can be quite complicated and it appears that observers establish category boundaries in an attempt to improve accuracy, but this increase in precision is purchased at the expense of bias. Psychophysical experimentation with graphical elements can provide interesting information for the study of graphical perception and can also illuminate basic processes in perception and cognition.