On Dec. 7, 1972, Cmdr. Eugene Cernan and his crew gazed out the hatch of their moon-bound spacecraft and saw what looked like a dazzling blue marble floating against the blackness of space. "We're not the first to discover this," Cernan radioed back to Mission Control, "but we'd like to confirm, from the crew of Apollo 17, that the world is round."
Then they snapped a picture of it.
By the time of the Apollo space program, the Earth's surface had been described by countless mapmakers from ancient to modern times. But until Apollo 17's "Blue Marble" photograph, taken from 18,000 miles in space, no one had ever seen the whole Earth at one time.
It's fitting that this image, which marked a milestone in the history of the art and science known as cartography, should be one of the highlights of Maps: Finding Our Place in the World, a stunning exhibition tracing the evolution of maps and mapmaking that opens today at the Walters Art Museum.
The show, organized by the Field Museum and the Newberry Library in Chicago, presents more than 100 of the world's greatest cartographic treasures including ancient Babylonian and Roman maps, Lewis and Clark's 19th-century surveys of the Western Territories and Charles Lindbergh's chart of his 1927 solo flight across the Atlantic.
One of the most intriguing questions raised by the exhibition has to do with how social, political and cultural conventions determine what qualifies as a map. The decisions cartographers make about what to include and what to leave out -- no map can show everything -- tell us as much about who they were as about the geography they describe.
Wandering through this massive show, one eventually concludes that the "world" we live in is as much a social as a geographical concept. And because maps help orient us in relation to the things that are important to us -- be they on a local, national, global or cosmic scale -- they offer a vivid portrait of the people who make and use them.
Take the diminutive map of the world created by Beatus Liebana, an eighth-century Spanish monk who pictured the world as an ellipse turned on its side enclosing three continents -- Africa, Asia and Europe -- separated by a central Mediterranean sea.
While by modern standards Liebana's placement of the oceans and land masses is wildly inaccurate, it served well as a spatial illustration of the scriptural cosmology Liebana wished to represent, in which the Earth's geographical features are merely the temporal stage on which the drama of God's plan unfolds.
Liebana's map reflected the medieval world he knew, the world of Christian redemption and salvation, and it offered a guide for the soul's journey from this world to the next.
The seafaring explorers of the Age of Discovery, by contrast, needed maps to navigate their way across vast oceans, and for this they required representations of the world that could be interpreted in terms of wind direction and compass headings.
One of the most important maps in the Walters show is the one produced by Gerard Mercator, a Flemish surveyor, instrument maker and map engraver who, in 1569, published the first projection map of the Earth's surface that correctly indicated compass points for ships at sea.
Though Mercator's projection distorted the size of the continents near the poles, his map represented a breakthrough in the technique of representing the Earth's curved surface on a flat sheet of paper and remained popular well into the 20th century.
Artists were often employed as map-makers, and the Walters show includes two maps by one of the greatest draftsmen of all time, the Italian Renaissance artist Leonardo da Vinci.
In his map of central Italy from around 1502, da Vinci represented various terrain features in darker or lighter tints, depending on their elevation. In doing so, he anticipated the modern practice of representing different elevations in different colors by more than 300 years.
The show also includes many examples of maps used for tracking phenomena invisible to the eye, such as Benjamin Franklin and Timothy Folger's 1783 map of the Gulf Stream's currents and Matthew Fontaine Maury's 1851 chart showing the global distribution of sperm whales. Franklin created his map when he was postmaster general of the fledgling U.S. and became concerned over the slow mail delivery between Europe and America.
A historically significant map of this type was British physician John Snow's map tracking the outbreak of cholera in central London in 1855. Snow had noticed that the deaths clustered around a neighborhood water pump from which residents regularly drank. He asked authorities to shut down the pump and the number of deaths immediately subsided. This led him to speculate that cholera was a water-borne disease.
Not all maps, of course, are intended to represent real places or even real things. Don't leave the Walters without checking out the show's delightful selection of maps describing wholly imaginary realms dreamed up by some of the world's best-known authors, from Sir Thomas More's Utopia and Robert Lewis Stevenson's Treasure Island to Lyman Frank Baum's Land of Oz and William Faulkner's Yoknapatawpha County.
If you already love maps, this show will be pure enchantment. If you haven't yet got the map bug, this is your chance. There are so many intriguing, surpassingly lovely examples of the cartographer's art here that in the end you may be persuaded, as I was, that looking at maps really is another way of looking at ourselves, and finding something beautiful there.