Mass-radius diagram of Neptunian planets with mass and radius known to better than with 20% precision. Green, orange, and red disks corresponds to planets in the Savanna, Ridge, and Desert, respectively. Blue (resp. magenta) background color defines the low-(resp. high) density classes. From left to right, dashed lines indicate iso-density curves at 0.2, 0.5, 1.0, 2.0, 3.5 g cm^-3