The visual language of information design is socially and rhetorically constructed, and like other forms of visual language (architecture, product design) is shaped by conventional codes that derive from the historical, cultural, aesthetic, and disciplinary conditions in which forms are invented, deployed, and reproduced. Sometimes brie y, sometimes over long stretches of time, conventions establish among their communities of users a viable level of circulation, which can be as local as a café menu or as global as a pie chart or a public information sign. Although conventional forms can mature into predictable patterns of use, their stability can be deceptive: as social constructs, conventions are always contingent and provisional – evolving, mutating, declining, and being reinvented – and subject to shiing and emerging communities and their shared values, knowledge, and technology (Kostelnick and Hassett 2003, 10-42; see also Kress and van Leeuwen 1996).