I wondered if I could add virtual fields to the feature tables of a number of polygon layers in a QGIS 3 project (or a geopackage).
As an example, I would like to add the virtual field
area (km²) as
round($area/1000000, 2) to ten polygon layers stored in a geopackage.
Is there a QGIS way of doing it? If not, any leads if I do this from R? (I don't use Python.)