[Qgis-user] question on scale bar world map

[Gabriel Cotlier]

Thanks to all. I currently have installed QGIS 3.34. I do not know the
validity of this map from MATLAB at :
https://la.mathworks.com/help/matlab/ref/geoaxes.html
but I was thinking of a map like this one, just without the small map in
the upper right corner and the division of countries in QGIS. I do not know
if that woud be possible and if so, if that scale bar in the figure below
makes any sense?
Thanks a lot again.


[image: image.png]

On Fri, Jun 27, 2025 at 2:22 AM Andreas Neumann <andreas at qgis.org> wrote:

> 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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