Thanks everyone for the explanations; they were very helpful and insightful. Regards, Gabriel
On Fri, Jun 27, 2025 at 8:35 AM Richard Duivenvoorde <[email protected]> wrote: > Hi Gabriel, > > Disclaimer: a lot of GEO-nerds here, he :-) > > But: given the perimeter on the equator of the earths is about 40000 km, > as you can see in your image, the scale bar is 'sort of valid' on the > equator, but totally OFF if you look near the poles (where the perimeter of > the earth is probably a fraction of the 10000 km scale). > > So: in general in such (global) maps you should not use a scalebar, but on > local level (where you use proper crs's and the unit's are meters), you > SHOULD always use a scalebar :-) > > And yes: do blame Matlab for his error from us ;-) > > Regards, > > Richard Duivenvoorde > > On 27-06-2025 12:55, Gabriel Cotlier via QGIS-User wrote: > > 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 < > 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.png > > > > On Fri, Jun 27, 2025 at 2:22 AM Andreas Neumann <[email protected] > <mailto:[email protected]>> 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 > < > 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 < > [email protected] <mailto:[email protected]>> wrote: > > > > Gabriel and list, > > > > > > > > On Thu, Jun 26, 2025, 16:05 Gabriel Cotlier via QGIS-User < > [email protected] <mailto:[email protected]>> 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 < > 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. > > _______________________________________________ > > QGIS-User mailing list > > [email protected] <mailto:[email protected]> > > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user < > https://lists.osgeo.org/mailman/listinfo/qgis-user> > > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > > > > > > > > -- > > > > -- > > Andreas Neumann > > QGIS.ORG <http://QGIS.ORG> board member (treasurer) > > > > > > _______________________________________________ > > QGIS-User mailing list > > [email protected] > > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > >
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