Equirectangular projection: Difference between revisions

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Revision as of 06:47, 9 May 2025

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The {{lang|fr|plate carrée}} ([[French language|French]], for ''flat square''),<ref>{{Cite web |title=Plate Carrée - a simple example |last=Farkas |first=Gábor |work=O’Reilly Online Learning |date= |access-date=31 December 2022 |url= https://www.oreilly.com/library/view/practical-gis/9781787123328/Text/b21938a9-09f7-46fa-b905-58a0a4ed7d8f.xhtml}}</ref> is the special case where <math>\varphi_1</math> is zero. This projection maps ''x'' to be the value of the longitude and ''y'' to be the value of the latitude,<ref>{{cite book |url=https://books.google.com/books?id=-FbVI-2tSuYC&pg=PA119 |page=119 |title=Geographic Information Systems and Science |author1=Paul A. Longley |author2=Michael F. Goodchild |author3=David J. Maguire |author4=David W. Rhind |publisher=John Wiley & Sons |year=2005|isbn=9780470870013 }}</ref> and therefore is sometimes called the latitude/longitude or lat/lon(g) projection. Despite sometimes being called "unprojected",{{by whom|date=December 2022}} it is actually projected.{{cn|date=December 2022}}

When the <math>\varphi_1</math> is not zero, such as [[Marinus of Tyre|Marinus]]'s <math>\varphi_1=36</math>,<ref>''Flattening the Earth: Two Thousand Years of Map Projections'', John P. Snyder, 1993, pp.&nbsp;7, {{ISBN|0-226-76747-7}}.</ref>, the [[Gall isographic projection]]'s <math>\varphi_1=45</math>, or Ronald Miller's <math>\varphi_1=(37.5, 43.5, 50.5)</math>,<ref>{{cite web |title=Equidistant Cylindrical (Plate Carrée) |url=https://proj.org/operations/projections/eqc.html |website=PROJ coordinate transformation software library |access-date=25 August 2020}}</ref> the projection can portray particular latitudes of interest at true scale.

While a projection with equally spaced parallels is possible for an ellipsoidal model, it would no longer be equidistant because the distance between parallels on an ellipsoid is not constant. More complex formulae can be used to create an equidistant map whose parallels reflect the true spacing.