In interaction design as in any design discipline, sketching serves several purposes.
It is a way to think. Ideas develop and grow in the conversation between eye and hand. Sketching is not merely a matter of documenting images that are already complete in the mind's eye. Thinking occurs, quite literally, in the manual actions involved in creating the sketch.
It is a way to communicate. Design ideas are made available for others' inspection, appropriation, criticism and development.
It is a way to persuade. Other stakeholders in the design process may be convinced of the value of a design idea through sketches.
There are, of course, many requirements that could be posed on sketching techniques. Here, I focus on the demands that sketching techniques be expressive (to explore the envisioned use situation in some detail), sketchy (to reflect the tentative nature of the ideas), and versatile (to handle a wide range of use situations including mobile use in physically demanding environments, for instance).
Interaction design is about shaping the digital material, which is a strange material in the sense that it is equally spatial and temporal. The use qualities of a digital design product are not determined only by its static appearance but equally by its behavior in interaction over time, by its dynamic Gestalt. Sketching techniques for interaction design need to handle this dual nature of the material.
The following sections illustrate a number of sketching techniques for interaction design. Examples are mostly drawn from design work that I have been involved in.
To section on USER INTERFACE SKETCHES.
Further thoughts on the role of sketching and the nature of the digital design material can be found in Löwgren and Stolterman (2004) Thoughtful interaction design: A design perspective on information technology (Cambridge, Mass.: MIT Press).