An atlas for Tolkien's world; The Atlas of Middle Earth, by Karen Wynn Fonstad. Boston: Houghton Mifflin Company $14.95

Fans of J. R. R. Tolkien -- especially those who like maps -- will find this book in valuable. The author, a cartographer, has devised an atlas of all the places mentioned in "The Silmarillion," "The Hobbit" and "The Lord of the Rings" trilogy. She has done a masterful job.

In addition to area maps, there are charts of migrations, of troop movements, of the routes taken by the Ring Fellowship; layouts of man-made and natural features such as Moria and Mt. Doom; and a section of thematic map illustrating climate, vegetation, population, and languages.

Portraying the geography of Tolkien's world demanded information from the real world as well.For instance, in depicting Arda the author needed to determine the size of Belegaer (The Great Sea). She knew Ar-Pharazon's armament needed 39 days to reach Valinor. By Comparison, Columbus crossed the Atlantic, covering 75 to 100 miles d aily. Using such facts she arrived at a solution.