This represents the diagrams of two large separable permutations, taken uniformly at random: for each $$i$$, there is a dot at coordinates $$(i,\sigma(i))$$. It converges towards a Brownian limiting object, that we called Brownian separable permuton. See details in the following article:

The Brownian limit of separable permutations, with Frédérique Bassino, Mathilde Bouvel, Lucas Gerin and Adeline Pierrot, submitted, arXiv.