[Qgis-user] question on scale bar world map

[chris hermansen]

Gabriel and list,


On Thu, Jun 26, 2025, 16:05 Gabriel Cotlier via QGIS-User <
qgis-user at lists.osgeo.org> wrote:

> Dear QGIS Users,
> I have been trying to do a world map with a scale bar and found the
> problem that needs a global projection, such as Greenwich for instance then
> the "scale bar" displayed in the map of the layout is for instance, 0.2 m
> in length but visually not consistent at all with the size of the
> continents and distances of the world map displayed.
>
> How could a world map with a scale bar be produced such that the scale bar
> length and size look consistent with the length and size of a world map in
> QGIS?
>

Gabriel, the usual problem with trying to do a scale bar on a global map is
that you have projected the spherical (more or less) globe onto a flat map.

This entails some serious distortion of the surface of the earth.

You are hoping for a projection that preserves distances at all points on
the map.

You may wish to read this Wikipedia article on map projections.

https://en.m.wikipedia.org/wiki/Map_projection

Another visual device that one sometimes sees is several "stacked" scale
bars, one for each 10 degrees or so of latitude, which of course isn't
feasible when the two points to be measured are at different latitudes.


Chris Hermansen · clhermansen "at" gmail "dot" com

C'est ma façon de parler.
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