Nikon L31 has a 16.0MP 1/2.3' (6.17 x 4.55 mm ) sized CMOS sensor . On the other hand, Kodak Astro AZ651 has a 21.0MP 1/2.3 (6.17 x 4.55 mm ) sized CMOS sensor .
Kodak Astro AZ651's sensor provides 5MP more than Nikon L31'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 L31 and Astro AZ651 sensor size comparison.
Nikon L31 and Kodak Astro AZ651 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.