This question already has an answer here:
Rookie Question! I have a shapefile in QGIS 1.8.0 of a country with 20000 divisions. I need the area of each division, but this is not a given attribute. When i click on a district, the "Identify Results" panel shows a "Derived" value for the area of each district along with the feature id. Can somebody tell me how I could extract these area values to a data file? Thanks!!