Freehand gestural interaction with direct-touch computation surfaces has been the focus of significant
research activity recently. While many interesting gestural interaction techniques have
been proposed, their design has been mostly ad-hoc and has not been presented within a contructive
design framework. In this paper, we develop and articulate a set of design principles for
constructing - in a systematic and extensible manner - multi-hand gestures on touch surfaces that
can sense multiple points and shapes, and can also accommodate conventional point-based input.
To illustrate the generality of these design principles, a set of bimanual continuous gestures
that embody these principles are developed and explored within a prototype tabletop publishing
application. We carried out a user evaluation to assess the usability of these gestures and use the
results and observations to suggest future design guidelines.