Nikon D80 has a 10.0MP APS-C
(23.6 x 15.8 mm ) sized CCD sensor . On the other hand, Sony RX100 II has a 20.0MP 1-inch
(13.2 x 8.8 mm ) sized BSI-CMOS sensor .
Sony RX100 II's sensor provides 10MP more than Nikon D80's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the D80 and RX100 II sensor size comparison.
As seen above, Nikon D80 has a 3.2x Larger sensor area than Sony RX100 II. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Nikon D80 and Sony RX100 II sensors have been tested by DxO and the results show that RX100 II has a better overall score of 67, 6 points higher compared to D80's score of 61.
Sony RX100 II