Information displays should be annotated, combining words, images, graphics, whatever it takes to describe and explain something. Annotation calls out and explains information and, at the same time, explains to viewers how to read data displays. Good annotation is like a knowledgeable expert/teacher at the viewer's side pointing and saying, "Now see how this works with that, how this might explain that..."
Yehudi Menuhin, a great violinist, marked up a score for Bach's Sonata No. 2 for Solo Violin. Penciled annotations show real-time performance strategies. To outsiders, insider markups appear chaotic and cryptic, but these personal annotations are for Menuhin's eyes, the only eyes that matter. All can learn from this useful workaday grid strategy: a relevant and intense data layer can become a coherent substrate scaffold upon which to overlay additional information. Maps do this all day long.
This order is all composed of movement and change, and although it is life, not art, we may fancifully call it the art form of the city and liken it to the dance—not to a simple-minded precision dance with everyone kicking up at the same time, twirling in unison and bowing off en masse, but to an intricate ballet in which the individual dancers and ensembles all have distinctive parts which miraculously reinforce each other and compose an orderly whole. The ballet of the good city sidewalk never repeats itself from place to place, and in any one place is always replete with new improvisations.