A descriptive model of visual scanning.

When designing a representation, a designer implicitly formulates a sequence of visual tasks required to understand and use the representation effectively. This paper aims to make the sequence of visual tasks explicit, in order to help designers eliciting their design choices. In particular, we present a set of concepts to systematically analyze what a user must theoretically do to decipher representation. The analysis consists of a decomposition of the activity of scanning into elementary visualization operations. We show how the analysis applies to various existing representations, and how expected benefits can be expressed in terms of elementary operations. The set of elementary operations form the basis of a shared, common language for representation designers. The decomposition highlights the challenges encountered by a user when deciphering a representation, and helps designers to exhibit possible flaws in their design, justify their choices, and compare designs.