Clumping noise: instances gather in patches with clearings between them.
Size of the patches, in metres (noise wavelength).
0 = no clumping, 1 = nothing at all in clearings. Values between thin clearings out partially.
0..1: the share of land that is clearing. 0.5 = about half the ground is in a patch.
Clumping noise: instances gather in patches with clearings between them.