1. Introduction
Mixed media interfaces combine physical media, such as posters, notebooks, and paper maps with digital content. Currently, few guidelines exist as to when and how to mix media. Approaches vary in how physical and digital content are integrated visually (e.g. through juxtaposition, or indirect linking via referent cues), structurally (e.g. through ad hoc digital annotation of physical media, or the use of physical media as an organizing dimension for digital content), and interactively (e.g. by providing a magic lens overlay, or interacting with physical media by pointing or other gesture).