Community Portal Site

We were also exploring a bit with the enterprise site template "Community Portal".  What we are trying to understand is that logic is being used behind the scenes for dictating the order in which individual community sites show up.  Apparently its due to some popularity indicator.  We have not been able to tell what that is yet. For example one community site that does not have content and little visits is showing up first while another community site with a lot of visits and content is showing up third on the list.  Any insights will be appreciated, we have been searching Microsoft official documentation but have not yet found and answer.