> @dkillick @pp-mo could you unpack 'linthresh'

I kind-of don't agree with this, because I think it is trying to explain the API of SymLogNorm, which is not appropriate unless maybe for something not properly documented.

We should restrict ourselves to describing what we are doing with it in our code.
So, I think _if you look at the documentation of SymLogNorm_, it should _then_ be clear why the usage does what we say it does.

But I will try and make the purpose clearer...