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| Gall–Peters projection | |
|---|---|
| Name | Gall–Peters projection |
| Type | cylindrical equal-area |
| Author | James Gall; Arno Peters |
| Introduced | 1855; 1974 (popularized) |
| Aspect | equatorial |
| Properties | equal-area |
Gall–Peters projection is a cylindrical equal-area map projection that presents the world with preserved area relationships while distorting shapes, directions, and distances. The projection attracted wide attention after Arno Peters popularized it in 1974, following earlier work by James Gall in 1855, provoking debate across institutions such as United Nations, Greenpeace, and National Geographic Society. It has been adopted in curricula, exhibitions, and by governments including United Kingdom, India, and Sweden for its perceived thematic equity.
The projection traces to James Gall who described cylindrical equal-area formulations in the mid‑19th century, contemporaneous with developments by Carl Friedrich Gauss and exchanges in periodicals of the Royal Geographical Society. Arno Peters reintroduced the projection in 1974 amid cultural debates of the Cold War and postcolonial discourse associated with organizations like UNESCO, Oxfam, and United Nations Conference on Trade and Development. Advocacy by activists from Amnesty International and educators in Brazil, South Africa, and Mexico amplified its use in classrooms and political posters alongside campaigns led by Noam Chomsky critics and proponents such as Mike Kidson and Richard Saul Wurman. Institutions including The Guardian, The Times, and The Economist covered ensuing controversies involving National Geographic Society and mapmakers such as Mercator, Petrus Plancius, and Gerardus Mercator.
Mathematically the projection is a cylindrical equal‑area mapping related to formulas by Johann Heinrich Lambert and J. P. Snyder. For geographic longitude λ and latitude φ the forward equations use a standard parallel φ0 = 45°N/S so that x = k(λ − λ0)cosφ0 and y = k sinφ/ cosφ0, where k is a scaling constant tied to earth radius choices used by International Association of Geodesy and by datum authorities like WGS84 and NAD83. The inverse mapping employs trigonometric inversion similar to methods applied in deriving the Lambert cylindrical equal-area projection, and implementations often reference algorithms from cartographers such as John P. Snyder and software projects like PROJ and GDAL.
The projection is equal‑area: regions on maps have areas proportional to their true areas on ellipsoids defined by standards like WGS84. Preserving area aligns with thematic needs championed by groups such as United Nations Development Programme, World Bank, and UNICEF for representational equity. It is neither conformal nor equidistant: angular relationships common in projections used by Mercator and Transverse Mercator are not preserved, affecting navigation favored by navies like the Royal Navy and firms such as Esri. Shape distortion increases poleward, producing elongated appearances for regions near Greenland, Antarctica, and Siberia—a concern cited by cartographers including Harold Fisk and commentators in Scientific American.
Adoption occurred in academic settings at universities such as Harvard University, University of Oxford, and University of Cape Town for courses in geography and development studies alongside materials from Oxfam and Amnesty International. Municipal and national bodies including city planners in Bristol and education ministries in Ethiopia and Brazil have employed the projection for posters and atlases. Nonprofit organizations like Greenpeace and World Wildlife Fund used it for emphasizing global inequities, while publishers such as Penguin Books and map vendors like Rand McNally and Ordnance Survey have produced Gall–Peters themed products. Digital implementations appear in GIS platforms including QGIS, ArcGIS Online, and visualization libraries supported by Mapbox and Leaflet.
Critics from academic cartography circles, including John P. Snyder and commentators at National Geographic Society, argued the projection was promoted with political rhetoric rather than cartographic neutrality, comparing it to older projections by Mercator and earlier equal‑area schemes by Lambert and Authalic constructions. Debates involved media outlets such as BBC News, The New York Times, and Der Spiegel and figures like Jacques Bertin and David Rumsey. Technical criticisms note severe shape distortion, compromised bearings relevant to Royal Geographical Society and International Hydrographic Organization standards, and pedagogical concerns raised by educators at institutions such as Teachers College, Columbia University. Supporters responded citing social justice aims aligned with United Nations sustainable development dialogues and campaigns by Amnesty International.
Variants include adjusted standard parallels (commonly 37.5°–52°) used by cartographers in atlases from Penguin Books and by GIS practitioners at Esri and in software libraries like PROJ and GDAL. Implementations range from paper atlases by publishers including Cassell and Oxford University Press to digital tiling via Web Mercator-based map servers adapted by Mapbox and Google Maps for thematic layers. Technical libraries and repositories on platforms like GitHub host code examples; academic treatments appear in works by John P. Snyder, Monmonier, and Mark Monmonier discussing projection selection, while open data initiatives by OpenStreetMap communities provide user-generated renditions.