Mapmaking activity usually increases in times of war. In the modern world maps have become indispensable to the conduct of military operations. Maps are often also used to report war news to the population at large, to rally popular support for war aims, or to enhance understanding of the geographical context of those aims. During World War II, for example, Rand McNally published a number of inexpensive wall maps and "war atlases" that were designed to help Americans follow the course of the war. It also added maps and other features to its regular line of atlases that reflected wartime concerns and interests.

World maps, such as our core map, showing the world centered on the North Pole, were first popularized by Richard Edes Harrison, a graphic artist, designer, and cartographer who made maps for Fortune, a popular magazine of business and political affairs. Harrison's version of the polar map was first published in August 1941 in an issue of Fortune that discussed the possibility of American involvement in the war that had been raging for two years in Europe, Asia, and Africa. Harrison felt very strongly that the rectangular world maps most familiar to Americans, showing the North Pole at the top, were ill-suited for the coming conflict. Traditional north-at-the-top world maps (like those in most common use in schools today) show the Americas in apparent isolation from the rest of the world-separated from Europe and Africa by the broad expanse of the Atlantic Ocean, and from Asia and Australia by the even larger Pacific Ocean. Harrison was convinced that such maps conditioned Americans to think that North America was well protected from attack because it appeared to be so far away from the rest of the world. For his most famous map, titled "One World, One War," Harrison chose a projection that put the North Pole at the center. This polar-centered map showed in dramatic fashion that the main land areas of the world are nearly continuous, rather than separated. Seen from a theoretical point above the North Pole, the Arctic Ocean appears as a smallish sea, rather like the Caribbean Sea, which barely separates the mass of Eurasia from the northern islands of Canada. This perspective made the main theater of war in Europe suddenly look very much closer to the United States and Canada, and the outcome of the conflict that much more important to Americans, too. Japan's long conflict with China also looked far more important, once Americans learned that it was taking place just over the horizon from Alaska. This shift in perspective was particularly important, Harrison and other war observers thought, because the airplane was proving to be a powerful and terrifying tool of warfare, capable of bombing civilian populations and war-related factories well behind the front lines. The icy seas of the Arctic Ocean were formidable barriers to maritime military operations, but could be fairly easily crossed by airplanes.

Harrison's revolutionary map quickly became popular among an anxious American citizenry nervously anticipating the consequences of total war. After Pearl Harbor in December 1941, Fortune issued the map separately for general sale. The U.S. Army ordered 18,000 copies, and the map quickly became a bestseller among average Americans forced by war to reeducate themselves in the finer points of geography. Other map publishers soon issued polar maps of their own. Rand McNally published its version of the polar map for the first time in 1942. Our core map is a later version of the Rand McNally polar map from the 1944 edition of its World Atlas, Premier Edition. The accompanying text echoes Harrison's sentiments. "The current Global War is rapidly forcing us to revise many of our pat, smug concepts inherited from the past," the atlas text declares. "Among these ideas destined for the scrap pile is that of a predominantly east and west world, with Europe essentially east of the United States and Asia to the westward…. The advent of the airplane and radio requires a new approach to the earth, one based on the shortest distance and directions between points in question." (For a full transcript of the atlas text accompanying the map, see Resources.) To underscore this last point, Rand McNally has drawn several red lines that represented the air distances between selected cities, for example, between Chicago and Berlin and Chicago and Tokyo.

The technical name for the projection Harrison and Rand McNally used is the North Polar Azimuthal Equidistant Projection. Azimuthal equidistant projections arrange the surface of the earth around a single central point, in this case the North Pole. All equal distances measured in any direction from that point appear as equal distances on the map. For example, a straight line drawn on the map from the North Pole to a point in Europe that is 2000 miles from the pole will be the same length as lines drawn from the pole to points 2000 miles away in North America, Asia, or the Pacific Ocean. On such maps, the shapes and relative sizes of the lands and water bodies near the central point are close to their actual shapes and relative sizes. Hence Europe and North America appear roughly in their correct relative position and proportion to each other. Places far away from the central point, however, are greatly enlarged and distorted in every way except in terms of their distance from the central point. Thus, Australia appears like a great flattened pancake at the upper left of the map, and in South America, Brazil and Argentina also appear greatly enlarged and fatter from east to west than we are accustomed to see them. The map has been cropped to eliminate the worst area of distortion, Antarctica, which is shown on a separate inset map.

In the northern hemisphere the red lines on the maps indicating the distances between cities approximate what are known as great circle routes. A great circle is an imaginary line drawn on the surface of a sphere that marks the intersection of the sphere with a plane that bisects the sphere. A great circle thus traces the circumference of a sphere at its maximum extent. All meridians are great circles, and so is the Equator (since it bisects the Earth). Other parallels of latitude, however, are not great circles, as they grow smaller as they approach the poles. Lines drawn on great circles trace the shortest distance between any two points on the surface of the globe. Hence, sea and air routes tend to follow great circles as much as possible. When one flies from Chicago to London, for example, one follows a great circle that takes the traveler northeast over Labrador and Greenland then southeast over the North Sea to the British Isles. Such a route seems nonsensical on a typical north-at-the-top world map, but makes more sense on our core map. Technically, the only great circles that should truly appear as straight lines on this projection are the meridians, since these show the travel in any direction from the central point of the projection. On this projection, the other great circles should, in actuality, be curved in some way, less so in the Northern Hemisphere near the pole, and much more so as we approach and pass the Equator. (A projection which shows all great circles as straight lines is called a gnomonic projection.) For illustrations and descriptions of these and other projections, see the websites and books of mapping listed in Resources.