Here's how Simon Elvery, the site's creator, explains it:
The suggested words appear in the order in which Google suggests them and are each connected by a line of varying thickness representing the number of search results you could expect if you did a Google search on the phrases which that word, its predecessors and ancestors in the tree would create.
And here's the lovely patterns he's picked out:
There are some recurring themes which have emerged as I've been playing with the site during its creation. Among other things, it seems people do rather a lot of searching on the topics of music, religion and relationships.
Sometimes the results are sad, like the people searching for free ebooks on relationships for dummies, and sometimes hopeful like looking for love.
Health is also a recurring theme with the names of medicines, diseases and symptoms appearing over and over again.
These would be hard to pick out--much less spot interrelations--without the Web site. Which is the calling card of any good infographic. Just perfect.