In webspeak, a referrer is a site that refers its readers to another site via hyperlinks. The posting of those links may be a conscious act on the part of a site's operators, or it may be the work of a contributing reader, and as such may not constitute an endorsement. That said, the study of referrers can reveal the pathways along which information of all sorts moves. In the present instance, I made use of the free referrer data provided by similarweb.com. For any given site SimilarWeb reveals what they believe to be the top five referrers to the site, as well as the top five sites the target refers their own readers to. In the graph below, the arrows indicate the direction of the referral. The snowball method was used to identify new sites to add to the data until I hit the point of diminishing returns.

By way of example

The graph seen here is available as a vector-based PDF, and also as an edgelist.