Another form of 2-dimensional art is illustration. Illustration comes in many forms, including books (and children's books in particular), posters, murals (again), decoration, advertising, poetry, and even mapwork.
Comes to mind the memorable illustrations from my childhood, in Mother Goose: so many poems, and most of them had a skillful and charming line-illustration in accompaniment. There were long, puffy skirts, ruffly, broad-brimmed bonnets, excellent animals, some of whom who talked, pretty English-style trees on the horizon, and of course to top it all off, Mother, with her ringlets, riding on the bridled Goose.
Illustrations can also come in novels, to mark the onset of certain chapters, and can be simple but well-designed graphics in a woodcut style print, in black and white only. This spring I've enjoyed reading the novel "Cross Creek," from the '30's if I remember right, by Marjorie Kinnan Rawlings, (she was the author of "The Yearling"). This book contained a lovely bunch of these black-and-white illustrations, picturing the "swamp" country in Florida, and which additionally kept me enthralled the whole time!