A DECADE AGO, the Library of Congress paid $10 million to acquire the only known original copy of a 1507 world map that has been called "the birth certificate of America." The large map, a masterpiece of woodblock printing, has been a star attraction at the library ever since and the object of revived scholarly fascination about the earliest cartography of the New World. The research has also rescued from obscurity a little-known Renaissance man, the 16th-century globe maker Johannes Schöner, who was responsible for saving the map for posterity.

We call ourselves Americans today because of the map's makers, Martin Waldseemüller and Mathias Ringmann, young clerics in the cathedral village of St.-Dié, France. By incorporating early New World discoveries, their map reached beyond the canonical descriptions of Old World geography handed down from Ptolemy in the second century. On a lower stretch of the southern continent, the mapmakers inscribed the name "America" in the mistaken belief that Amerigo Vespucci, not Columbus, deserved credit for first sighting a part of that continent, South America.

Or possibly they favored Vespucci because he held more firmly to the growing consensus that this was indeed a New World, not the Indies (as Columbus so wanted to believe), and because he wrote more colorfully than Columbus about the people he encountered.

The map is also the source of an abiding mystery. How did Waldseemüller and Ringmann already know so well the configuration of South America, before any recorded Spanish or Portuguese voyages around the horn to the west coast? How did they know of the Pacific before Balboa made his sighting in 1513? Hard to believe it was just a guess or futuristic vision of what world geography would come to be.

Were the cartographers themselves dropping a hint when they wrote on the map that "if you are not familiar with the new discoveries, do not be afraid of what it is you see on this map, for it is how you will come to see your world in the future"?

Five years ago, John W. Hessler, a historian of cartography at the library, published "The Naming of America," an account of the map's importance in post-Ptolemy geography, its disappearance for centuries and its rediscovery in a castle near the Black Forest in southwestern Germany. Now, Dr. Hessler has dug deeper into the dynamic of the years between Columbus, in 1492, and Copernicus, in 1543. Science and exploration were stretching minds to distant horizons, once unknown. Copernican astronomy was about to dislodge Earth from the center of the universe, a start to the Scientific Revolution.

His new book, "A Renaissance Globemaker's Toolbox," is not able to solve the mapmakers' enduring mystery. But it is a richly illustrated delight to the eye. I advise a slow tour of the maps, drawings, marginal notes and other material remains of Schöner's wide-ranging mind. Read the informative captions, then begin the text.

General readers will find the accounts of Schöner's place in history and the preservation of the map lucid and fascinating. Parts of more technical chapters, like the instructions on making a terrestrial globe, appear to be written more for the author's academic peers than for many laypeople. And of necessity, this is hardly a flesh-and-blood biography, as the archives are largely silent about Schöner's personal life.

We do see a print of a bearded, heavyset man and read a brief diary entry about him as a young Catholic cleric with a relaxed view of celibacy: he entered into a relationship with a woman that produced three children. One can thus understand his conversion to Protestantism in Martin Luther's Reformation. That led him to the professorship in mathematics at Nuremberg, which he held to his death in 1547.

Dr. Hessler leaned heavily on Schöner's personal archive of correspondence and manuscripts, books and maps, including corrections and comments in the margins. He was into everything in science: completing two world globes in his prime, drawing celestial maps and globes and preparing horoscopes, one even for a Hapsburg emperor. Not another Leonardo da Vinci, but who was?

"Rather than a producer of theories," Dr. Hessler observes, Schöner "was instead a disseminator, a compiler and a transmitter of the new science and mathematics." Yes, something of a pack rat, but one with a sharp eye for what was likely to be of importance in the future. This attribute cast Schöner as savior of the 1507 world map. His practice was to gather and bind portfolios of his compiled materials. One of these, now called Schöner Sammelband (meaning "gathering"), preserved the "America" map. There it passed from hand to hand, all the other original prints disappeared, and Schöner's was lost for more than 300 years. Most of the bound portfolios wound up in a Vienna library, but one languished in a German castle, unrecognized, until a Jesuit priest found it in 1901 — thence to the United States in 2003.

Nothing in the book points up more clearly Schöner's pivotal place in a world in transition from the medieval to the modern than his residual interest in astrology and his awakening curiosity when he apparently heard reports of a new theory being formulated by a Polish Catholic cleric. A brilliant young student of Schöner's, Georg Joachim Rheticus, went to see Copernicus in 1539 and learned more about the Earth orbiting the Sun. Rheticus then composed a short treatise, written in the form of a letter to his teacher, "most illustrious and learned" Johannes Schöner.

The publication, widely circulated in Europe, was the first definitive account of the new Copernican system of the heavens.