[Qgis-user] question on scale bar world map

[Andreas Neumann]

Hi all,

Chris explained why it is impossible to have a consistent scale for a world
projection on a 2D flat plane.

The good news is, that in QGIS 3.44 there is a setting to influence the
scale calculation method: see
https://www.qgis.org/project/visual-changelogs/visualchangelog344/#application-and-project-options

Best regards,
Andreas

On Fri, 27 Jun 2025 at 02:37, chris hermansen via QGIS-User <
qgis-user at lists.osgeo.org> wrote:

> 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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-- 

--
Andreas Neumann
QGIS.ORG board member (treasurer)
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