View source for Gall–Peters projection

{{Short description|Cylindrical equal-area map projection}}
[[File:Gall–Peters projection SW.jpg|upright=1.3|thumb|The Gall–Peters projection of the world map]]
The '''Gall–Peters projection''' is a rectangular, [[Equal-area projection|equal-area]] [[map projection]]. Like all equal-area projections, it distorts most shapes. It is a [[cylindrical equal-area projection]] with latitudes 45° north and south as the regions on the map that have no distortion. The projection is named after [[James Gall]] and [[Arno Peters]].

Gall described the projection in 1855 at a science convention and published a paper on it in 1885.<ref name="Gall">{{Cite journal | last1 = Gall | first1 = James | year = 1885 | title = Use of cylindrical projections for geographical, astronomical, and scientific purposes | url = http://publikationen.ub.uni-frankfurt.de/files/9461/E001639254.pdf| journal = Scottish Geographical Magazine | volume = 1 | issue = 4| pages = 119–123 | doi = 10.1080/14702548508553829 }}</ref> Peters brought the projection to a wider audience beginning in the early 1970s through his "Peters World Map". The name "Gall–Peters projection" was first used by [[Arthur H. Robinson]] in a pamphlet put out by the American Cartographic Association in 1986.<ref name="ACA1986">American Cartographic Association's Committee on Map Projections, 1986. ''Which Map is Best'' p. 12. Falls Church: American Congress on Surveying and Mapping.</ref>

The Gall–Peters projection achieved notoriety in the late 20th century as the centerpiece of a controversy about the political implications of map design.<ref name="Crampton">{{Cite journal | last1 = Crampton | first1 = Jeremy | year = 1994 | title = Cartography's defining moment: The Peters projection controversy, 1974–1990 | journal = Cartographica | volume = 31 | issue = 4| pages = 16–32 | doi=10.3138/1821-6811-l372-345p}}</ref>

==Description==
[[Image:Tissot indicatrix world map Gall-Peters equal-area proj.svg|thumb|upright=1.3|The Gall–Peters cylindrical equal-area projection with [[Tissot's indicatrix|Tissot's indicatrices]] of deformation]]
===Formula===
The projection is conventionally defined as:

:<math>\begin{align}
  x &= \frac{R\pi\lambda\cos 45^\circ}{180^\circ} = \frac{R\pi\lambda}{180^\circ\sqrt{2}}\\
  y &= \frac{R\sin \varphi}{\cos 45^\circ} = R \sqrt{2} \sin \varphi
\end{align}</math>

where ''λ'' is the longitude from the central meridian in degrees, ''φ'' is the latitude, and ''R'' is the radius of the globe used as the model of the earth for projection. For longitude given in radians, remove the {{sfrac|{{pi}}|180°}} factors.

===Simplified formula===
Stripping out unit conversion and uniform scaling, the formulae may be written:

:<math>\begin{align}
  x &= R\lambda\\
  y &= 2R\sin\varphi
\end{align}</math>

where ''<math>\lambda</math>'' is the longitude from the central meridian (in radians), ''<math>\varphi</math>'' is the latitude, and ''R'' is the radius of the globe used as the model of the earth for projection. Hence the sphere is mapped onto the vertical cylinder, and the cylinder is stretched to double its length. The stretch factor, 2 in this case, is what distinguishes the variations of cylindric equal-area projection.

===Relation to cylindric equal-area projections===
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. The standard parallels of the Gall–Peters are 45°&nbsp;N and 45°&nbsp;S. Several other specializations of the equal-area cylindric have been described, promoted, or otherwise named.<ref name="Snyder2">Snyder, John P. (1989). ''An Album of Map Projections'' p. 19. Washington, D.C.: U.S. Geological Survey Professional Paper 1453. (Mathematical properties of the Gall–Peters and related projections.)</ref><ref name="Monmonier">Monmonier, Mark (2004). ''Rhumb Lines and Map Wars: A Social History of the Mercator Projection'' p. 152. Chicago: The University of Chicago Press. (Thorough treatment of the social history of the Mercator projection and Gall–Peters projections.)</ref><ref name="Smyth">Smyth, C. Piazzi. (1870). ''On an Equal-Surface Projection and its Anthropological Applications''. Edinburgh: Edmonton & Douglas. (Monograph describing an equal-area cylindric projection and its virtues, specifically disparaging Mercator's projection.)</ref>

==Origins and naming==
The Gall–Peters projection was first described in 1855 by the Scottish clergyman [[James Gall]], who presented it along with two other projections at the Glasgow meeting of the [[British Association for the Advancement of Science]] (the BA). He gave it the name "orthographic" and formally published his work in 1885 in the ''Scottish Geographical Magazine''.<ref name="Gall"/> The projection is suggestive of the [[Orthographic projection (cartography)|orthographic projection]] in that distances between parallels of the Gall–Peters are a constant multiple of the distances between the parallels of the orthographic. That constant is {{radic|2}}.

In 1967, the German filmmaker [[Arno Peters]] independently devised a similar projection, which he presented in 1973 as the "Peters world map". Peters's original description of his projection contained a geometric error that, taken literally, implies standard parallels of 46°02′&nbsp;N/S. However the text accompanying the description made it clear that he had intended the standard parallels to be 45°&nbsp;N/S, making his projection identical to Gall's orthographic.<ref name="Maling">Maling, D.H. (1993). ''Coordinate Systems and Map Projections'', second edition, second printing, p. 431. Oxford: Pergamon Press. {{ISBN|0-08-037234-1}}.</ref> In any case, the difference is negligible in a world map.

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.<ref name="ACA1986">American Cartographic Association's Committee on Map Projections, 1986. ''Which Map is Best'' p. 12. Falls Church: American Congress on Surveying and Mapping.</ref> Before 1973 it had been known, when referred to at all, as the "Gall orthographic" or "Gall's orthographic". Most Peters supporters refer to it as the "Peters projection". During the years of [[#Peters world map controversy|controversy]], the cartographic articles tended to use one name or the other, while acknowledging both names. In recent years "Gall–Peters" seems to dominate.{{Citation needed|date=April 2024|reason=cf https://books.google.com/ngrams/graph?content=Gall+projection%2Cgall+map%2CPeters+projection%2Cpeters+map%2CGall-Peters+projection%2Cgall-peters+map&year_start=1800&year_end=2019&corpus=en-2019&smoothing=3&case_insensitive=true}}

==Peters world map controversy==
[[File:Peters projection mural.jpg|thumb|Mural at a school depicting the Gall–Peters projection, with [[continent]]s coloured.]]
[[File:Peters projection, date line in Bering strait.svg|thumb|upright=1.3|The right and left borders of the Peters map are in the [[Bering Strait]], so all of Russia is displayed on the right side. 
{{legend|#00b400|Greenwich great circle}}
{{legend|#c80000|Bering Strait great circle (traversing [[Florence]] in Italy, see [[Florence meridian]])}}]]
The Gall–Peters projection initially passed unnoticed when presented by Gall in 1855. It achieved more widespread attention after Arno Peters reintroduced it in 1973. He promoted it as a superior alternative to the commonly used [[Mercator projection]], on the basis that the Mercator projection greatly distorts the relative sizes of regions on a map. In particular, he criticized that the Mercator projection causes wealthy Europe and North America to appear very large relative to poorer Africa and South America.<ref name="Monmonier"/>{{rp|155}} These arguments swayed many socially concerned groups to adopt the Gall–Peters projection, including the [[National Council of Churches]]<ref>{{cite web|url=http://www.ncccusa.org/news/01news13.html|title=Ncc Friendship Press' Peters Projection Map}}</ref> and the magazine ''[[New Internationalist]]''.<ref>{{cite web|url=  http://www.newint.org/features/1983/05/01/flat/|title= The New Flat Earth|date=May 1983}}</ref>

His campaign was bolstered by the inaccurate claim that the Gall–Peters projection was the only "area-correct" map.<ref name="Bulletin">(1977) ''The Bulletin'' 25 (17) pp. 126–127. Bonn: Federal Republic of Germany Press and Information Office.</ref><ref name="Snyder165">Snyder, John P. (1993). ''Flattening the Earth: Two Thousand Years of Map Projections'' p. 165. Chicago and London: The University of Chicago Press. {{ISBN|0-226-76746-9}}. (Summary of the Peters controversy.)</ref> In actuality, some of the oldest projections are equal-area (such as the [[sinusoidal projection]]), and hundreds have been described. He also inaccurately claimed that it possessed "absolute angle conformality", had "no extreme distortions of form", and was "totally distance-factual".<ref name="Bulletin"></ref> Peters framed his criticisms of the Mercator projection with criticisms of the broader cartographic community. In particular, Peters wrote in ''The New Cartography'',

{{Blockquote|By the authority of their profession [cartographers] have hindered its development. Since Mercator produced his global map over four hundred years ago for the age of Europeans world domination, cartographers have clung to it despite its having been long outdated by events. They have sought to render it topical by cosmetic corrections.…

The cartographic profession is, by its retention of old precepts based on the Eurocentric global concept, incapable of developing this egalitarian world map which alone can demonstrate the parity of all peoples of the earth.<ref name="Peters">Peters, Arno (1983). ''Die Neue Kartographie/The New Cartography'' (in German and English). Klagenfurt, Austria: Carinthia University; New York: Friendship Press.</ref>}}

As Peters's promotions gained popularity, the cartographic community reacted with hostility to his criticisms, as well as to the inaccuracy and lack of novelty of his claims.<ref name="Snyder157">Snyder, John P. (1993). ''Flattening the Earth: Two Thousand Years of Map Projections'' p. 157. Chicago and London: The University of Chicago Press. {{ISBN|0-226-76746-9}}.</ref> They called attention to the long list of cartographers who, over the preceding century, had formally expressed frustration with publishers' overuse of the Mercator and advocated for alternatives.<ref name="Edwards">Edwards, Trystan (1953). ''A New Map of the World''. London: B.T. Batsford LTD.</ref><ref name="Hinks">Hinks, Arthur R. (1912). ''Map Projections'' p. 29. London: Cambridge University Press.</ref><ref name="Steers">Steers, J.A. (1927). ''An Introduction to the Study of Map Projections'' 9th ed. p. 154. London: The University of London Press.</ref><ref name="Kellaway">Kellaway, G.P. (1946). ''Map Projections'' p. 37–38. London: Methuen & Co. LTD.</ref> In addition, several scholars criticized the particularly large distortions present in the Gall–Peters projection, and remarked on the irony of its 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.<ref name="Snyder CC">{{Cite journal | last1 = Snyder | first1 = J.P. | year = 1988 | title = Social Consciousness and World Maps |url=https://www.religion-online.org/article/social-consciousness-and-world-maps/ | journal = Christian Century | volume = 105 | pages = 190–192 }}</ref><ref name="Robinson1985">{{Cite journal | last1 = Robinson | first1 = Arthur H. | year = 1985 | title = Arno Peters and His New Cartography | journal = American Cartographer | volume = 12 | issue = 2| pages = 103–111 | doi=10.1559/152304085783915063}}</ref>

The increasing publicity of Peters's claims in 1986 motivated the American Cartographic Association (now [[Cartography and Geographic Information Society]]) to produce a series of booklets (including ''Which Map Is Best''<ref name="ACA1986"/>) 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 a resolution rejecting all rectangular world maps, a category that includes both the Mercator and the Gall–Peters projections,<ref name="Robinson1990">{{Cite journal | doi = 10.1111/j.0033-0124.1990.00101.x | last1 = Robinson | first1 = Arthur | year = 1990 | title = Rectangular World Maps—No! | journal = Professional Geographer | volume = 42 | issue = 1| pages = 101–104 }}</ref><ref name="AmericanCartographer">''American Cartographer''. 1989. 16(3): 222–223.</ref> though [[NACIS|the North American Cartographic Information Society]] notably declined to endorse it.<ref>{{Cite journal |last1=Wood |first1=Denis |author-link1=Denis Wood |year=2003 |title=Cartography is Dead (Thank God!)|journal=Cartographic Perspectives |issue=45 |pages=4–7 |doi=10.14714/CP45.497 |quote=Nearly the entire profession endorsed this idiotic resolution…(but not NACIS)|doi-access=free }}</ref>

The two camps never made any real attempts toward reconciliation. The Peters camp largely ignored the protests of the cartographers, and did not acknowledge Gall's prior work<ref name="Snyder165" /> until the controversy had largely run its course, late in Peters's life. While he likely devised the projection independently, his unscholarly conduct and refusal to engage the cartographic community undoubtedly contributed to the polarization and impasse.<ref name="Crampton"/>

In the ensuing decades, [[John Brian Harley|J. Brian Harley]] credited the Peters phenomenon with demonstrating the social implications of map projections.<ref name="Harley">{{Cite journal | last1 = Harley | first1 = J.B. | year = 1991 | title = Can There Be a Cartographic Ethics? | journal = Cartographic Perspectives | volume = 10 | issue = 10| pages = 9–16 | doi = 10.14714/CP10.1053 }}</ref>

== Adoption ==
Maps based on the projection are promoted by [[UNESCO]], and they are also widely used by British schools.<ref>Higgins, Hannah B. ''The Grid Book''. Cambridge, Massachusetts: MIT Press, 2009. {{ISBN|9780262512404}}  p.94. "Embroiled in controversy from the start, the map is nonetheless widely used in the British school system and is promoted by the United Nations Educational and Scientific Cultural Organization (UNESCO) because of its ability to communicate visually the actual relative sizes of the various regions of the planet."</ref> The U.S. state of [[Massachusetts]] and [[Boston Public Schools]] began phasing in these maps in March 2017, becoming the first public school district and state in the [[United States]] to adopt Gall–Peters maps as their standard. Until its dissolution in 2020, [[Amherst, Massachusetts|Amherst]]-based ODT Maps Inc. was the exclusive North American publisher of Peters and [[Hobo–Dyer projection]] maps.<ref name="guardian-19mar2017">{{cite news|author1=Joanna Walters|title=Boston public schools map switch aims to amend 500 years of distortion|url=https://www.theguardian.com/education/2017/mar/19/boston-public-schools-world-map-mercator-peters-projection|access-date=March 19, 2017|newspaper=[[The Guardian]]|date=March 19, 2017}}</ref><ref>{{cite news|title=ODT’s proportionate world maps find a fan in ‘Don the donor’|first=Sophia|last=Gardner|work=[[Daily Hampshire Gazette]]|location=Northampton, Massachusetts|date=August 2, 2021|url=https://www.gazettenet.com/ODTMaps-hg-073121-41713808|archiveurl=https://web.archive.org/web/20210803033521/https://www.gazettenet.com/ODTMaps-hg-073121-41713808|archivedate=August 3, 2021}}</ref><ref>{{cite web|title=About Us|publisher=ODT Maps|location=Amherst, Massachusetts|date=2021|url=https://manywaystoseetheworld.org/pages/about-us|archiveurl=https://web.archive.org/web/20210222040848/https://manywaystoseetheworld.org/pages/about-us|archivedate=February 22, 2021}}</ref> On April 16, 2024, [[Nebraska]] Governor [[Jim Pillen]] signed a law that requires public schools to display maps based on the Gall–Peters projection, a similar [[cylindrical equal-area projection]], or the [[AuthaGraph projection]] beginning in the 2024–2025 school year.<ref>{{cite news|title=More than 100 bills sent to Nebraska Gov. Pillen for approval in legislative voting spree|first=Zach|last=Wendling|work=[[Nebraska Examiner]]|publisher=States Newsroom|date=April 11, 2024|url=https://nebraskaexaminer.com/2024/04/11/more-than-100-bills-sent-to-nebraska-gov-pillen-for-approval-in-legislative-voting-spree/}}</ref><ref>{{cite act|type=Legislative Bill|index=1329|legislature=Nebraska Legislature|article-type=Section|article=90|date=2024|pages=102–103|url=https://nebraskalegislature.gov/FloorDocs/108/PDF/Final/LB1329.pdf#page=102}}</ref><ref>{{cite web|title=LB1329|work=Nebraska Legislature|publisher=Nebraska Legislature|location=Lincoln, Nebraska|date=April 18, 2024|accessdate=May 15, 2024|url=https://nebraskalegislature.gov/bills/view_bill.php?DocumentID=55393}}</ref>

== See also ==
* [[List of map projections]]
* [[Gall stereographic projection]]: another of Gall's projections.
* [[South-up map orientation]]

== References ==
'''Notes'''
{{Reflist|30em}}

'''Further reading'''
* Snyder, John P. (1987), ''Map Projections—A Working Manual:  U.S. Geological Survey Professional Paper 1395'', Washington:  Government Printing Office.  https://pubs.er.usgs.gov/publication/pp1395.

== External links ==
{{Commons category|Gall-Peters projection}}
* [https://web.archive.org/web/20121105052519/http://articles.timesofindia.indiatimes.com/2005-05-27/edit-page/27845927_1_map-india-countries The Size of the Matter]—An article in ''[[The Times of India]]'' on why the Gall–Peters projection should be more widely used.
* [http://geography.about.com/library/weekly/aa030201a.htm Peters Projection vs. Mercator Projection] {{Webarchive|url=https://web.archive.org/web/20160410053632/http://geography.about.com/library/weekly/aa030201a.htm |date=2016-04-10 }}—A critique of the importance of the Gall–Peters projection.

{{Map projections}}
{{Authority control}}

{{DEFAULTSORT:Gall-Peters projection}}
[[Category:Cylindrical equal-area projections]]
[[Category:20th-century maps and globes]]
[[Category:1885 introductions]]