I am working through "Learn QGIS" for 3.4. Under populating attribute data (pg 62) instruction say to use Field Calculator to populate area field of the attribute table. Following instructions to the letter, I hit OK on the Field Calculator and, while the button appears to be active, nothing changes in the attribute field. Is this a glitch?
I you have already an area field and you need to populate it with area calculation you need to select the field first as you can see in the red box, write
$area after the equal sign (blue box ) and select Update all (pink box):
The area field will be populated: