[Qgis-user] Help with scales in print layouts for geographic CRS

[Nyall Dawson]

On Wed, 6 Apr 2022 at 09:34, Greg Troxel via Qgis-user
<qgis-user at lists.osgeo.org> wrote:
>
> Jorge Gustavo Rocha via Qgis-user <qgis-user at lists.osgeo.org> writes:
>
> > I need you help to understand how scale works with geographic
> > coordinate systems.


In all cases (projected OR geographic) the scalebar logic is:

1. Create a horizontal line across the width of the layout map
2. Calculate the length of that line using great circle/ellipsoidal
calculations, based on the project's ellipsoid settings.
3. Compare the length of the ellipsoidal line vs the map width to
calculate the corresponding scale

So qgis scalebar calculations are ALWAYS based on great
circle/ellipsoidal lengths*.

Nyall

* Unless the project itself is set to not use ellipsoidal calculations
and only use planar calculations, in the project properties dialog