Sona are sand drawings used by the Cokwe people of Angola in storytelling. Some of the simpler drawings are done by tracing closed curves around a rectangular array of points. Interesting questions arise when one investigating these figures, including greatest common divisor and sums of arithmetic sequences. Sona can also be translated into graphs (in the mathematical graph theoretic sense), which offers more opportunities for exploration.
Most of the material in this lesson is taken from "Drawings from Angola: Living Mathematics" by Paulus Gerdes, published by Lulu.com and available from amazon.com.