Mapmaking: synthesis of wonder and science; The Mapmakers, by John Noble Wilford. New York: Alfred A. Knopf. $20.

Anyone who has hiked in a wilderness area knows the value of an accurate map. It is nt something that can be taken for granted; sometimes a life depends on it. But in the beginning the whole world was wilderness. Early man had nothing to guide him but common sense and an instinct, John Noble Wilford asserts, for "spatial relatedness."

How that instinct matured into geography is the subject of Wilford's "The Mapmakers," a massive and informative popular history. The book has only one drawback: Sometimes the mass of information bogs down the narrative. For the most part, however, it is engaging reading, deftly organized around two compeling themes.

According to Wilford, mapmaking is a synthesis of wonder and science, a naive curiosity to explore space and increasingly accurate methods and instruments to measure it. Wilford's cast of characters who attempted to satisfy that curiosity includes Ptolemy, Newton, Cassini, and Mercator. And here, too, are Columbus, Lewis land Clark, John Wesley Powell, and Captain Cook. Some have taken the measure of earth from their backyard; some have made the earth their own backyard. The most intrepid of these was Cook, who said he wanted to go "not only farther than any man has been before me, but as far as I think it is possible for any man to go."

"The Mapmakers" is beautifully illustrated. From front cover to back, it is filled ith maps ranging from the earliest known (made in ancient China) to Mercator's first projections, to Landsat images of earth from outer space and computer-generated "thematic" maps of global resources. The most eye-catching of the illustrations are not so much scientific as artistic, however -- maps from medieval and early Renaissance Europe, whose empty areas where Africa and Asia should be are filled with fancifully drawn elephants, smug-looking caliphs, and mysterious names of kingdoms that never existed.

The fantastic geography of the Middle Ages, Wilford points out, was also responsible for making Columbus look so original. Long before 1492, Ptolemy had not only insisted the earth was round, but the Greek Eratosthenes fairly accurately guessed its circumference by some simple measurements and experiments with the angles thrown by sundials at various points in Egypt. Columbus's originality, Wilford argues, lay in the courage to act on such ideas and plummet into the unknown.

If not Columbus, it is Cook who towers above the other mapmakers in Wilford's study. In the first place, Cook was not only a great seaman, but an expert surveyour and cartographer. Some of his charts, which Wilford reproduces here, give fairly accurate portrayals of the coasts of Newfound- land, New Zealand, and Australia. In the second place, Cook's voyages put to rest what Wilford calls the "two greatest geographical illusions": the legends of a sub-Arctic "northwest passage" and a "Terra Australis," or a land mass in the Southern Hemisphere equal in size to the land masses of the north. When Cook reached 70 degrees south and saw only ice floes, the story was dead. As Wilford comments, "Pioneer mapmakers sometimes erase as much from the map as they add to it."

Wilford, a science correspondent with the New York Times, also deals at length with theoretical aspects of mapmaking: problems of projection, the attempts to fix accurate measure for a degree of latitude, the debate between Newton and the Cassinis about the shape of the earth (not round, but spheroid), and the discovery of a timepiece accurate enough to determine longitude. As Wilford makes clear, moreover, all this is not old history. The discovery of the volcanic activity in the cleft of the mid-Atlantic ridge in the 1950s revived an old theory that the Americas, Europe, and Africa once fitted together and are now drifting apart. In short, as Wilford details, undersea mapping gave birth to a whole new view of the earth, the "plate tectonics" that now dominates geology.

Wilford also adds an account of his own involvement with Bradford Washburn of the Boston Museum of Science on a mapmaking expedition in the Grand Canyon in 1972. This account is broken up into vignettes that preface major sections of the history. They help change the tempo somewhat and relieve the slight drag of the chronology. They provide a personal touch, moreover, that underlines the basic strength of "The Mapmakers:" Wilford's strong sense of the drama of ma n and space.

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