FOSS gamedev and creative worlds

l use perlin noise to detect whether the position at x and z belong to the sumpf biome.
https://github.com/HybridDog/sumpf/blob ... n.lua#L127
To allow custom biome sizes and rarity, l need to find out how to predict the noise values occurrences. Simply using sinus doesn't work right.

p(v) is the chance the abs of a randomly picked value is smaller than v.
p(0) = 0 of course,
p(1) ≈ 1 (The values are not always inside [-1; 1].)
p(0.5) > 0.5 l assume

How can l calculate p(v)?

I'd like to know this too. For example what noise thresholds to use if i want to divide a world equally into 3 biomes.
It's easy to calculate the maximum noise value from octaves and persistence though.

l made a mod to collect the values and show their distribution in a picture: https://github.com/HybridDog/pnoiseana

Yeah i researched this on the net and analysing large numbers of calculated results seems the easiest way.