Sorry for commenting again but I think there is a way for you to do this in a completely open, easy, and privacy-preserving way. You don’t need to access their database.

1. Get a list of instances that you want to look at the subscription patterns for. (All the instances here + Lemmy.world)

2. Go to that instance’s website, click the “Communities” tab at the top, and then click “All” It shows how many users from that instance are subscribed to that community (both communities from that instance and outside of that instance)

If you find a way to automatically (or manually) scrape this data from all of those websites you can create the visualization that you were talking about.

So you were right, the data is open source it is just specific to each website.

No problem just notify me if you ever decide to follow through.

If you are interested there is a professor named Damon Centola that might be interested in dedicating time to gathering that data and might help with the visualization as well. If you are in the sociologist space or just interested you could reach out to him.

Personally I would love to see this kind of project done. But for it to work most people on the servers data that you are working with would have to be informed and given time to answer. I hope you reach out to the administrators of each instance and ask them if they would be ok with this and give them time to ask their users. Knowledge is power and if the visualization was public I think it could be helpful.