The first chapter, 'The Route to Regular Division', describes Escher's early artistic development, and how Escher first became intrigued by the problem of filling the plane with interlocking shapes (tessellation). This work came to dominate his art from 1937. He was also encouraged, by a half-brother who was a professor of geology, to study papers on symmetry by Pólya and other mathematicians in the Zeitschrift für Kristallographie. These helped launch Escher into his own detailed investigations of the rules for generating the allowable patterns for tiling the plane.