Among the Chokwe of eastern Angola, a story worth telling was worth drawing. The teller smooths a patch of sand, presses in a rectangular grid of dots with the fingertips of both hands, and then, while speaking, runs a fingertip through the sand in one swift continuous line that weaves around the dots, rebounds at the edges, and closes on itself as the story ends. The drawing is a lusona; the plural is sona; and the men who commanded the full repertory, the akwa kuta sona, were respected specialists whose skill was proof of memory, dexterity and standing.
Sona served as mnemonics and as teaching. Many belong to fables and proverbs; others carried lessons of the mukanda, the initiation school through which boys became men, and those meanings were the school's to give, so that the drawings public visitors saw were the surface of a deeper instruction, and parts of that depth are described in the literature only in outline, as is proper. The tradition was documented by ethnographers from the early twentieth century onward, by which time colonial disruption had already thinned it: the mission schools and labour regimes that broke the mukanda's rhythm broke the drawings' transmission with it. Paulus Gerdes, the mathematician who devoted much of his career to sona, worked from those records and from surviving drawers to reconstruct the corpus, and his books are now among the fullest memorials of an African geometric art.