The Stanford Encyclopedia of Philosophy provides a list of related entries at the bottom of each entry. These relations aren’t always reciprocal (only 25 percent of these links are reciprocated). Sometimes, a more specific topic will link to a more general one, but not conversely (though often, the reason is less clear). These links form a directed graph, with the articles as nodes and the links as one-way edges connecting them.
You can start to get a sense of a large graph by asking about the paths you can trace through it. This site conducts a breadth-first search through this graph to find all shortest paths between any two nodes. You can do the same search ignoring that many links aren’t reciprocated, often with interestingly different results.
Graph visualization is notoriously difficult, but the Vega interactive visualization grammar I use on this site strikes a nice balance between expressiveness and ease of use.
There are many other excellent graph visualizations online, including in philosophy. I have collected some of these below. If you find more, let me know! Let's increase the graph density of the internet!
My first title for this project, “Six Degrees of Francis Bacon,” was already taken by the excellent historical social network reconstruction project of the same name.
The original. Often ridiculous, always fun.
Adam Edwards provides some interesting visualizations based on the Louvain community detection method for directed graphs at Visualizing the Stanford Encyclopedia of Philosophy.
Maximilian Noichl (University of Wien) applied a clustering algorithm called HDBSCAN on word frequencies to visualize clusters of related topics.
Mark Alfano and Moses Boudourides give you the largest strongly connected component of the graph at once. Yes, it's overwhelming, but zoom in!