ATLAS OF THE TRANSATLANTIC SLAVE TRADE. Edited by David Eltis, David Richardson. 336 pages. Yale University Press. $50.

It is very difficult to comprehend the cruelty, the magnitude of the deprivation, the crazy justifications and hard-hearted enforcement of what was essentially the largest global, unregulated free market system ever established during the pre-high-tech age: slavery.

The subject is fraught with challenges, not the least of which is conceptual.

A new "Atlas of the Transatlantic Slave Trade" and companion website, slavevoyages.org, reveal better than ever before the full scope of this international market system.

The trade, which began in 1501 and lasted until 1867, was the cause of the largest forced population displacement on record. More than 12.5 million captive Africans were transported to the New World, and several million more were relocated to other parts of the globe.

Within Africa, entire tribes were decimated, betrayed by African slave traders whose familiarity with local cultures made them ideal business partners of the Europeans. The need was for a work force so Europeans could purchase at affordable prices coffee, tobacco, cotton, indigo, rice and, especially, sugar (and its byproducts, such as molasses and rum), all cultivated in the New World.

The majority of slave voyages were organized by the Portuguese and British, but many more were arranged by the French, Spanish, Dutch, Danes and even Swedes, "Atlas" shows.

Around 46 percent of all slaves landed at ports in Brazil. By comparison, about 5 percent of all slaves arrived at ports in North America. South

Carolina accounts for just 2 percent of the total slave trade (though its port in Charleston was especially active from 1803 to 1807).

Sugar was by far the dominant economic motivator. A map in the book shows how the crop migrated from Indonesia through the Mediterranean basin and to the Atlantic Coast over the course of two millennia. By the 1500s, just as the Conquistadors were affecting the colonization of South and Central America, sugar was ready to cross the Atlantic. Coincidentally, water navigation and shipping technology had improved, and Europeans were better able to organize long voyages and trade goods between continents.

During the trans-Atlantic crossing, about 20 percent of all captives perished from violence and disease, "Atlas" says. Upon arrival, most of the Africans who survived -- those who died during a voyage were unceremoniously thrown overboard -- often were sold to a middleman, transported yet again, then resold. Many, weak and ill from the crossing, died during this final stage.

The Africans who survived were subjected to what was known as the "seasoning." If a captive managed to remain alive for the first two years in the New World, he was considered "seasoned," and his value went up. It is, therefore, remarkable that so many blacks endured, labored, reproduced and managed somehow to retain any of their cultural inheritance.

Visualizing slavery

The trans-Atlantic slave trade was so vast, its effects so devastating, that scholars typically study slavery according to their particular fields: economics, religion, language, agriculture or anthropology. Or they examine it according to geography to discover what exactly happened in Barbados, Brazil, Cuba or South Carolina.

But now, for the first time, the authors have created a work that enables us to visualize nearly every aspect of the forced migration of captive Africans during the course of four centuries, and this helps us conceptualize the enormity of the slave trade, as well as the reasons for it.

The "Atlas of the Transatlantic Slave Trade," co-edited by David Eltis and David Richardson, was meant to be a capstone to an equally astounding new website project, slavevoyages.org. But the "Atlas" stands on its own.

It began in the 1980s as a CD-ROM project, according to Eltis. Scholars had compiled data from a variety of independent sources and, with support from Cambridge University and the National Endowment for the Humanities, attempted for the first time to assemble it in one place.

"What emerged was the fact that there was a big hole in the South Atlantic," Eltis said.

Plenty of documentation existed concerning the triangular trade between Europe, Africa and the New World north of the equator (Caribbean, North America), but little could be found that described the enormous and long-lasting two-way trade between Africa and Brazil.

The Portuguese tended to outfit slaving expeditions from their colonies in Brazil, using "an out-and-back structure," Eltis said. "As a result of that, the records were not as rich." And what few records could be found were in Portuguese.

To fill the gaps in the historical record, Eltis and his colleagues secured new funding from the U.K., more from the NEH and other sources, and began to expand and transform the CD-ROM project into what became the "Voyages" database.

Recently, the team added the "Contribute" page to facilitate collection of new information from other scholars. "It operates like a journal," Eltis said.

Submissions are vetted and, if approved, incorporated into the data set when updates are scheduled every two years.

The "Atlas" consists of six parts illustrating the nations that transported slaves, the ports that outfitted voyages, the African coastal origins of slaves, the experience of the Middle Passage, the New World destinations for captives and the eventual suppression and abolition of the trade.

Essentially, a series of 189 beautifully rendered, crystal-clear maps, the book is enhanced with contextual information such as ship log entries, diary passages, old documents and illustrations, photographic and cartographic documentation, ship renderings, slave inventories and lists of the dead.

A foreword by David Brion Davis provides a concise, elegant and unsentimental framework in which the reader might conceptualize and interpret the many maps before him. Davis explains convincingly why the term "evil" must be applied to the practice of slavery, and how this vast international free-market system was essentially diminished and eventually stopped by the abolitionist movements in England and the United States.

Perhaps the book does not reveal much new information. Scholars who have studied slavery and the trans-Atlantic trade have had a good grip on the topic for decades. The project's great accomplishment is that it provides the first comprehensive overview of the entire trade from beginning to end along with an interactive, updatable database and website interface. Scholars can submit missing information or correct existing data, and users of the site have the ability to delve deeply into the trove of material and construct data sets.

The comprehensive nature of the project and the thoughtful contributions of its editors and essayists invite us to consider afresh this violent episode in world history and reflect on the consequences of unfettered markets, the human cost of slavery to both captives and captors and the true value of what have become staple crops: cotton, sugar and coffee.

Unfinished business

If the "Atlas" and "Voyages" website enable all of us to better appreciate the full scope of slavery, the comprehensive slavery project offers a unique opportunity to members of the African diaspora, for they are called upon to assist with the next phase. Eltis said. The "African Origins" website initiative is under way.

Like the "Voyages" site, this one is based on documentary evidence -- lists and lists of African names, 70,000 of them, taken from liberated ships during the abolitionist period. These records are digitized and published online, and now Eltis and his colleagues are asking blacks around the world to try to identify the individuals named.

A persistent challenge -- for blacks and for academia -- has been to determine where exactly in Africa members of the diaspora came from. The problem is made all the more difficult because of the great shuffling of Africans during the slave trade. Many captives from one region were taken to another on the continent, and many captives liberated by British ocean patrols after the 1807 abolition of the trade were returned to places far from home. Population displacement is not only a trans-Atlantic problem; all of western Africa was transformed by the practice of slavery.

The goal of "Origins," then, is to trace connections between descendants of captive Africans and their ancestors, zeroing in on specific areas of origin on the African continent.

Now the creators of the "Atlas of the Transatlantic Slave Trade" want to extend the collaboration far and wide. As they do so, new generations of historians will contribute to this essential effort to centralize information about one of the world's most catastrophic events.

People with African origins will have a chance to reconnect to the continent.

And the rest of us will gain a new appreciation for the global metamorphosis wrought by the violent removal of so many millions -- and the price all of us have paid for it.