The Gall-Peters projection is one specialization of a configurable equal-area map projection known as the equal-area cylindric or cylindric equal-area projection. The Gall-Peters achieved considerable notoriety in the late 20th century as the centerpiece of a controversy surrounding the political implications of map design. Maps based on the projection continue to see use in some circles and are readily available, though few major map publishers produce them.
where is the longitude from the central meridian in degrees, is the latitude, and is the radius of the globe used as the model of the earth for projection. For longitude given in radians, remove the /180° factors.
The various specializations of the cylindric equal-area projection differ only in the ratio of the vertical to horizontal axis. This ratio determines the standard parallel of the projection, which is the parallel at which there is no distortion and along which distances match the stated scale. There are always two standard parallels on the cylindric equal-area projection, each at the same distance north and south of the equator. The standard parallels of the Gall-Peters are 45° N and 45° S. Several other specializations of the equal-area cylindric have been described, promoted, or otherwise named.
|Specialization||Standard parallels N/S|
|Lambert cylindric equal-area||equator|
|Behrmann cylindric equal-area||30°|
|Craster rectangular equal-area||37°04'|
|Gall-Peters (= Gall orthographic = Peters)||45°|
The name "Gall-Peters projection" seems to have been used first by Arthur H. Robinson in a pamphlet put out by the American Cartographic Association in 1986.. Prior to 1973 it had been known, when referred to at all, as the "Gall orthographic" or "Gall's orthographic." Most Peters supporters refer to it only as the "Peters projection." During the years of controversy the cartographic literature tended to mention both attributions, settling on one or the other for the purposes of the article. In recent years "Gall-Peters" seems to dominate.
Peters's original description of the projection for his map contained a geometric error that, taken literally, imply standard parallels of 46°02' N/S. However the text accompanying the description made it clear that he had intended the standard parallels to be 45° N/S, making his projection identical to Gall's orthographic. In any case, the difference is negligible in a world map.
Arno Peters was the son of social activists and probably gained his lifelong concern about equality from his parents, Lucy and Bruno Peters. In 1929, when Peters was 13, the famous African American activist and NAACP field secretary William Pickens visited the family and left a signed copy of his book Bursting Bonds. During the Second World War, Peters' father was imprisoned by the Nazis for refusing to obey the totalitarian regime.
At first, Peters's foray into cartography was largely ignored by the cartographic community. Campaigns for new projections spring up now and then, rarely making much of an impression. For one thing, the mathematics that governs map projections does not permit development of a world map that is significantly better in any objective sense than the hundreds of map projections already devised. Peters's map was no exception in that regard, and in fact Peters had (probably unwittingly) based it on a projection which was already over a century old. That projection - Gall's orthographic - passed unnoticed when it was announced in 1855. For another thing, inappropriate use of the Mercator projection in world maps and the size disparities figuring prominently in Peters's arguments against the Mercator projection had been remarked upon for centuries and quite commonly in the 20th century. Even Peters's politicized interpretation of the common use of Mercator was nothing new, with mention of a similar controversy in Kelloway's 1946 text. Cartographers had witnessed a similar campaign twenty years prior to Peters's efforts when Trystan Edwards described and promoted his own eponymous projection, disparaging the Mercator, and recommending his projection as the solution. Peters's map differed from Edwards's only in height-to-width ratio. Cartographers, who had long despaired over publishers' stubborn use of the Mercator, had no reason to think Peters would succeed any more than Edwards had, or, for that matter, any more than any of his predecessors had.
Peters, however, launched his campaign in a different world than Edwards had. He announced his map at a time when themes of social justice resonated strongly in academia and politics. Insinuating cartographic imperialism, Peters found ready audiences. The campaign was bolstered by the innuendo that the Peters projection was the only "area-correct" map. Other claims included "absolute angle conformality," "no extreme distortions of form," and "totally distance-factual."
All of those claims were erroneous. Some of the oldest projections are equal-area (the sinusoidal projection is also known as the "Mercator equal-area projection"), and hundreds have been described, refuting any implication that Peters's map is special in that regard. In any case, Mercator was not the pervasive projection Peters made it out to be: a wide variety of projections has always been used in world maps. Hence, it could be argued that Peters had simply set up a straw man to knock down. Peters's chosen projection suffers extreme distortion in the polar regions, as any cylindric projection must, and its distortion along the equator is considerable. Several scholars have remarked on the irony of the projection's undistorted presentation of the mid latitudes, including Peters's native Germany, at the expense of the low latitudes, which host more of the technologically underdeveloped nations. The claim of distance fidelity is particularly problematic: Peters's map lacks distance fidelity everywhere except along the 45th parallels north and south, and then only in the direction of those parallels. No world projection is good at preserving distances everywhere; Peters's and all other cylindric projections are especially bad in that regard because east-west distances inevitably balloon toward the poles.
The cartographic community met Peters's 1973 press conference with amusement and mild exasperation, but little activity beyond a few articles commenting on the technical aspects of Peters's claims. In the ensuing years, however, it became clear that Peters and his map were no flash in the pan. By 1980 many cartographers had turned overtly hostile to his claims. In particular, Peters writes in The New Cartography,
This incendiary attack did not endear cartographers, who themselves had long been frustrated by the favoritism publishers showed for Mercator's projection.
The two camps never made any real attempts toward reconciliation. The Peters camp largely ignored the protests of the cartographers. Peters maintained there should be "one map for one world"—his—and did not acknowledge the prior art of Gall until the controversy had largely run its course, late in his life. While Peters likely reinvented the projection independently, the unscholarly conduct and refusal to engage the cartographic community undoubtedly contributed to the polarization and impasse.
Frustrated by some very visible successes and mounting publicity stirred up by the industry that had sprung up around the Peters map, the cartographic community began to plan more coordinated efforts to restore balance, as they saw it. The 1980s saw a flurry of literature directed against the Peters phenomenon. Though Peters's map was not singled out, the controversy motivated the American Cartographic Association (now Cartography and Geographic Information Society) to produce a series of booklets (including Which Map is Best) designed to educate the public about map projections and distortion in maps. In 1989 and 1990, after some internal debate, seven North American geographic organizations adopted the following resolution, which rejected all rectangular world maps, a category that includes both the Mercator and the Gall-Peters projections:
The geographic and cartographic communities do not unanimously disparage the Peters World Map. For example, one map society, the North American Cartographic Information Society (NACIS), declined to endorse the 1989 resolution, though no reasons were given. Some cartographers, including J. Brian Harley, have credited the Peters phenomenon with demonstrating the social implications of map projections, at the very least. Crampton sees the condemnation from the cartographic community as reactionary and perhaps demonstrative of immaturity in the profession, given that all maps are political. Denis Wood sees the map as one of many useful tools. Lastly, Terry Hardaker of Oxford Cartographers Limited, sympathetic to Peters's mission, became the map's official cartographer when Peters, overwhelmed by the technical aspects of cartography, sought to pass on those responsibilities.