The sentences

Letters are not yet writing. The 1446 book, after explaining each letter class, devoted a chapter to assembly: how letters pack into syllable blocks, blocks into words, words into sentences.

This part is gog’s assembly chapter, and it moves through six groups.

First the mechanics. The + operator layers marks in one panel, and the * operator derives a new statement from a mark and a transform. Position in the sentence then decides which layer a channel binds to. Second, one pair of operators with two uses. | and / split one plot into a grid of panels, and the same pair arranges separate plots on a page. Third, two of the picture-computing transforms: flow carries a magnitude through its stages, and cluster builds the tree that puts an axis in order.

Fourth come the coordinate spaces. space stands a flat plot up by adding a single vowel, z. polar bends the same plane into a circle. nest packs a panel into regions. map flattens the earth onto the page, and globe keeps it round. Those five ask nothing new of the sentence. network does ask something new: it places a graph with no axes at all, from a transform that lays out its nodes. Fifth is time, where play cuts the plot into frames and runs them in order. Last is your own choice: brush selects rows with the mouse, and the plot dims what you did not select.

One law holds this part together, Compositional Invariance: a composed expression means the same thing wherever it appears. What you build in one chapter can be carried into the next, and it still means the same thing. That is what makes sentences worth building.