diff --git a/doc/faq.md b/doc/faq.md index 06a0de23db..7f24caefa0 100644 --- a/doc/faq.md +++ b/doc/faq.md @@ -161,6 +161,22 @@ var swissCoord = ol.proj.transform([8.23, 46.86], 'EPSG:4326', 'EPSG:21781'); ## Why is the order of a coordinate [lon,lat], and not [lat,lon]? +Because of two different and incompatible conventions. Latitude and longitude +are normally given in that order. Maps are 2D representations/projections +of the earth's surface, with coordinates expressed in the `x,y` grid of the +[Cartesian system](https://en.wikipedia.org/wiki/Cartesian_coordinate_system). +As they are by convention drawn with west on the left and north at the top, +this means that `x` represents longitude, and `y` latitude. As stated above, +OpenLayers is designed to handle all projections, but the default view is in +projected Cartesian coordinates. It would make no sense to have duplicate +functions to handle coordinates in both the Cartesian `x,y` and `lat,lon` +systems, so the degrees of latitude and longitude should be entered as though +they were Cartesian, in other words, they are `lon,lat`. + +If you have difficulty remembering which way round it is, use the language code +for English, `en`, as a mnemonic: East before North. + +#### A practical example So you want to center your map on a certain place on the earth and obviously you need to have its coordinates for this. Let's assume you want your map centered on Schladming, a beautiful place in Austria. Head over to the wikipedia