The screen resolution of 3072x1920 (224.6ppi) is triple 1024x640.

Apple states that it also scales to

  •  1920x1200 (3:5)

  •  1680x1050 (48:25)

  •  1280x800  (12:5)

which obviously are all fractions. With the small pixel size (0.1122mm) it probably doesn't matter that much.

The 16" display has a 16:10 aspect ratio.