ABSTRACT
This chapter examines the factors that define, shape, and sustain visual genres as they evolve amid varying disciplinary, cultural, and political conditions. It focuses on a longstanding traditional form, mosaics, and their forerunners, rectilinear area charts. The chapter also focuses primarily on the historical evolution of area charts and mosaics, particularly in the nineteenth century. It explores the history of mosaics as a genre by examining several defining characteristics— formal, functional, social, cultural, and technical— that collectively establish genre identity and boundaries, however distinct or amorphous. Data displays function on a variety of levels, including their perceptual usability, how clearly and comfortably readers grasp the data envisioned, the purposes the displays serve in the situations in which they are deployed, and their rhetorical effects—persuasive, informative, emotive—in those situations. Mosaics also serve a variety of recurring rhetorical purposes, which illustrate a versatility that distinguishes them from other data display genres.
