Ask HN: Interesting JavaScript Migration Animation Seen Here

HN: Earlier this month there was a really interesting animation shown that modelled the migration between two cities (New York and SF or LA). You were able to control the rate at which each population migrated to the other and watch as an equilibrium has found.

I've tried every search phrase I can fathom both on this site's search and Google site search. Does anyone remember the site which had this beautiful animation? Would love to show this demonstration to my class.