A geologic interpretation of a 1:500 000 scale mosaic of optically correlated Seasat SAR imagery showed that 14 of the 17 major units mapped by the Geological Survey of Iceland could be recognized although it was not possible to close all the radar geologic boundaries. Interactive work with computer correlated imagery produced no additional information significant to mapping at that scale. Comparison with Landsat revealed that the radar produced more data on ice type, alluvial categories and upon lineaments but the overall interpretative value of Landsat was clearly the better of the two. The results of local co-registering Landsat and Seasat were interesting but did not cause any modification of the regional interpretation