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

[Jorge Gustavo Rocha]

Hi,

I need you help to understand how scale works with geographic coordinate 
systems.

For projected coordinates systems, the layouts seems to work as expected.

This is my use case:

I've draw a polygon with 1000m width and height, and another with 1500, 
width and height, sharing the upper left corner.

1) Using a projected CRS, if I create a layout with a 150mm x 150mm map, 
the 1500m polygon fits perfectly on the print area, setting a 1:10000 
scale. That's what I expected. The results is 
https://nextcloud.geomaster.pt/index.php/s/TKpkBaqty8BdLL8

2) Using a geographic CRS, the same 150mm x 150mm map, at the same 
1:10000 scale, the area is bigger then the 1500m polygon. The result is 
attached https://nextcloud.geomaster.pt/index.php/s/H2eAytsPANyxn6Y

On both layouts the scale bar widget is working properly. The distances 
(and areas) are properly calculated in QGIS interface. I have set the 
GRS 1980 ellipsoid for distance and area calculations.

My question is: why the second layout does not fit the 1500m polygon 
properly? The second layout shows approximately a 2000m square, instead 
of a 1500m square.

Regards,

Jorge Gustavo