Plus there are lots of constraints. People of the same generation have to appear on the same vertical level. And there are lots of configurations that are simply impossible to represent. For instance a couple with three kids, each of them marries someone, how do we represent the parents of who they marry without crossing lines? Or it is relatively easy to represent someone having children from two different wives but how about three different wives without crossing lines?<p>And then it needs to look reasonably compact to be visually helpful. So it&#x27;s a kind of a best effort basis.