Once for a review of a book about the Normandy invasion by John Keegan, who has written the introduction here, I went to the map room at the New York Public Library to get a better sense of the order of battle. Most anecdotes about the library pay it reverence, but not this one. First the librarian on duty scolded me for glancing through a newspaper. This, he said, was a room for maps. But when I asked for those that showed the placement of American and Canadian divisions on June 6, 1944, the best he could offer was a tourist brochure, printed in the 1950s, describing pastoral Normandy. It was the kind of leaflet found in motels near the registration desk, and no mention was made of history's largest amphibious landing that had passed through a decade earlier. No wonder the librarians discourage people from browsing in the collection.

The answer to my question, however, is supplied in the "Atlas of the 20th Century," a superb collection of maps illustrating military campaigns. In the pages explaining D-Day, for example, the landing beaches--Utah, Omaha, Gold, Juno and Sword--are marked clearly, as is the progress of all divisions involved that day. Subsequent maps diagram Germany's effort to push the Allies back into the sea, which failed, and the great sweeping engagement of Patton's Third Army toward Le Mans. The detail reaches to the regimental level--which unit took which town--and this precision is present in the explanations from the Boer War to the Falklands. In all, there are 166 entries.

The author, Richard Natkeil, is head of the Cartographic Department of The Economist, and for the past 15 years he has studied the campaigns of the two world wars. He was responsible for the maps in Purnell's "History of the Second World War." In the "Atlas of the 20th Century," he has told a history of the century in maps, mostly military, and written short, eloquent summaries of the battles. Of the Western Front at the end of 1916, he writes: "Around the Somme, where British casualties had amounted to no less than 1 percent of the entire British population, the Western Front had been pushed forward for just about six miles over an 18-mile length." Little wonder that Keegan writes in his introduction: " . . . of no subject are maps a better teacher than history."

Maps show the state of affairs at a precise moment in time, but they also hint at the future. The page showing the Treaty of Versailles speaks volumes for all that it explains about the origins of World War II. The Russian annexations in the Baltic states, following the Molotov-Ribbentrop Pact of 1939, are shown for what they were: aggression of a primitive and brutal kind. The partition of Palestine, explained in three maps, makes it clear why the violence continues today.

Having all these maps in one collection lets the reader make connections between campaigns separated by thousands of miles and decades of time. For example: the fighting on Okinawa along the Shuri Line resembled that in the mud of Passchendaele in World War I; the fight between Britain and Argentina for control of Falkland Sound was a tactical repeat of that between the Japanese and the U.S. Navy for The Slot off Guadalcanal; and the Japanese attack on the Russian squadron off Port Arthur in 1904 can be understood as a dress rehearsal for Pearl Harbor.

Spliced between the maps and text are well-chosen photographs that further distinguish the atlas. The explanation of the Battle of Jutland succeeds, in part, because of the photograph showing a squadron of German battleships in formation. Another photograph, from the First Battle of Ypres, shows the 2nd Batallion, of the Warwickshire Regiment, commuting to the front lines in London buses, thus adding irony and poignancy to Natkeil's observation that "trench warfare meant that the war had become a conflict between industries as well as between soldiers."

If the atlas has a flaw--either as a reference work or as an illustrated history--it is the few omissions that cannot be helped in a work of this magnitude. Peleliu, one of the worst battles in the Pacific campaign against the Japanese, escapes Natkeil's attention. Similiarly, at least for American readers, the war in Vietnam is given cursory treatment in three maps: one excellent description of Dien Bien Phu; another of the Tet offensive that serves to summarize most of the fighting; and one of the fall of Saigon. This would have been the place to attempt an understanding of American strategy, but apparently even in history the war in Vietnam defies the clear lines of explanation that allow Natkeil to explain El Alamein or Mao's Long March.

Nevertheless, the atlas is a triumph of clarity and detail. It can make sense of the Organization of Petroleum Exporting Countries, the siege of Stalingrad, and the Second Balkan War in 1913. Thus it ought to be of equal delight to admirals, armchair strategists, high school students and anyone else for whom history is a collage of maps.