Design for Information: An Introduction to the Histories, Theories, and Best Practices Behind Effective Information Visualizations

Trees can be many things: objects, art, symbols, or information. As objects, trees act as homes and shelter, they provide food and oxygen, and they bind soil to hold topography in place. You can read about this in any biology textbook. Trees have also had a long tradition in the visual arts. To me, perhaps the most interesting books about trees as art are those by Fowles and Horvat (1979) and by Shyam et al. (2006). The former is a disquisition by novelist John Fowles on the connection between the natural world and human creativity, accompanied by moody photographs of trees taken by Frank Horvat. The latter book is a series of hand-lithographed prints of tribal art images from three Gond people of central India (Bhajju Shyam, Durga Bai, and Ramsingh Urveti). (And yes, the land of the Gond is Gondwanaland, which was the source of our name for the southern land masses.) The most famous use of trees as symbols is the Tree of Life, which recurs in many cultures throughout the world, and which you can read about in Cook (1974). It often appears as a World Tree, which supports the heavens, thereby connecting the heavens, the human world, and (through its roots) the underworld. This motif has appeared in specific forms in many cultures, including Assyrian, Akkadian, Sumerian, Babylonian, Egyptian, Ancient Greek, Nordic (Norse), Celtic, Olmec, Aztec, Mayan, Buddhist, Tibetan, Hindu, and Siberian, among others. The Biblical Tree of Life, on the other hand, was actually the lignum vitae (Tree of Eternal Life) not the arbor vitae (Tree of Life). It was explicitly contrasted with the lignum scientiae boni et mali (Tree of Knowledge of Good and Evil), from which Adam and Eve ate the forbidden fruit, and were thereby ejected from Eden. This Biblical imagery was later co-opted as the arbor scientiae (Tree of Knowledge), starting with the Porphyrian tree in the third-century AD (although there are no extant copies from that time). That is, knowledge can often be arranged like the branches of a tree; and indeed, that metaphor has come down to us today when referring to the different “branches” of human knowledge (e.g., branches of science). For example, Joachim of Fiore used the tree as a metaphor for historical relationships in his Liber Figurarum of 1202 (Hestmark 2000), a book whose exquisite prints could easily have been included above under “art.” In his book Arbor Scientiae Venerabilis et Cælitus of 1295, Ramón Llull used the tree to illustrate the growth and inter-relationships of knowledge more generally (Gontier 2011; Kutschera 2011). It is with this role of trees as illustrations of information that the two review books concern themselves. They thus represent the latest manifestations of a very long tradition involving visualizations of human knowledge. The tree is probably the most ubiquitous and longlasting of our visual metaphors, illustrating the relations between objects as well as the relations between concepts. In the modern world the Tree of Knowledge has been greatly generalized, so that trees are now both visual and mathematical representations of the relationships among pieces of information. There is thus much that is new for these two authors to discuss, because computers and new algorithmic models have produced an array of new methods and designs. The book by Manuel Lima (The Book of Trees) focuses on trees exclusively, although some of them you may not have recognized as trees. The book is arranged by type of tree: Figurative trees, Vertical trees, Horizontal trees, Multidirectional trees, Radial trees, Hyperbolic trees, Rectangular treemaps, Voronoi treemaps, Circular treemaps, Sunbursts, and Icicle trees. A tree is defined as representing hierarchically structured information, and therefore any such representation can be called a “tree,” including things that look more like maps and Venn diagrams than like traditional trees. Each chapter is arranged chronologically, which acknowledges the historical milieu noted above (covering more than 500 years). This means that the information being represented is not arranged by context, and thus conceptual themes recur throughout the book rather than being consolidated. For example, phylogenetic trees have historically been drawn as figurative, vertical, horizontal, multidirectional, radial, or hyperbolic (the latter being restricted to interactive trees), and so phylogenetic trees are illustrated throughout the book. Moreover, some trees could easily fit into more than one chapter, such as the horizontal trees on pp. 98–101, which could as easily be seen as multidirectional. This means that the book provides only a visual overview of trees, rather than providing some sort of