Equirectangular projection: Difference between revisions

Revision as of 16:14, 3 January 2021

Revision as of 18:19, 3 January 2021

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The {{lang|fr|plate carrée}} ([[French language|French]], for ''flat square''), 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, and therefore is sometimes called the latitude/longitude or lat/lon(g) projection or is said to be “unprojected”. Despite sometimes being called “unprojected”, it is actually projected.

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> or [[Royal_Scottish_Geographical_Society|Ronald Miller]]'s <math>\varphi_1=(37.5, 43.5, 50.5)</math>,<ref>{{cite web |last1=PROJ Contributors |title=Equidistant Cylindrical (Plate Carrée) |url=https://proj.org/operations/projections/eqc.html |website=PROJ coordinate transformation software library |accessdateaccess-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.