Post, Walsum, Post, and Silver described some generic techniques to generate attribute sets and introduced a modelling language to create icons and to link the attributes to the icon parameters.
An icon shows essential characteristic of the data in the domain to which the icon refers. Most icons describe only data in a single point. However, icons can also describe small point sets. The second item on the left of the bottom row of the above image, for example, shows an interpolated tube through five points. The four top icons visualize the Jacobian of a velocity field, which is a tensor. The bottom left icon shows an average velocity arrow and a velocity distribution ellipsoid. The tensor probe is explained in image 2. The bottom right icon is a 3D Chernoff face, which is used to describe high dimensional data in an abstract data space, rather than in an Euclidean physical space.