Art of M.C. Escher, Page 5.

Once Escher developed his "layman's theory" for filling the plane with designs, he filled sketchbooks with drawings that combined his "tile" art with familiar scenes.  Often these scenes wer taken at interesting angles of perspective and the objects took on a three dimensional look through careful shading and positioning (Schattschneider, D., 2004, pp. 112-113).