First the explaining …
Since there were several queries about the meaning and significance of the connector lines, especially concerning S.u.S.E/Jurix and Maemo+Moblin/Meego, here’s a small legend.
… and then some observing
Comparing the GLDT with the recently introduced BSDT further down, there has been a remarkable explosion of diversity in the early nineties – when internet access started to become ubiquitous.
Also, looking at the latest version of the GLDT, we can observe gradual shifts in forking activity, starting with Red Hat and moving to Debian, then Knoppix, with a burst of Slackware derivatives in 2004 and finally Ubuntu taking the lead particularly in 2007.
Another less joyous observation is how the Knoppix family tree is slowly thinning, with no new additions in recent years. While Knoppix itself releases regularly, a lot of its offspring seems to have been less lucky.
Gentoo on the other hand appears to have more stable derivatives, albeit similarly rare in recent years, yet the distribution itself may have lost quite a bit of momentum.
I conclude with the remark that while Fedora’s subtree of direct forks looks comparatively small, keep in mind that a lot of Red Hat based distros have switched to Fedora (and Red Hat itself too, actually), as seen by the large number of connectors in the full GLDT.