Chia Network has released a very detailed image showing a dashboard of the current state of Chia nodes and it is fascinating. It is, from my understanding the first real glimpse into the details of the Chia network itself. The data is almost certainly gathered from the introducer that the Chia client speaks to when booting up.
Gene had this to say about how they classify the various nodes:
reachable means we can connect to them but they’re full (not on that dashboard right now). Reliable is that they have open ports and are ones that the DNS introducer will hand outGene Hoffman, President and COO Chia Network
Basically this is a good idea of how they decide how to hand out IPs when a new client boots up. They know that the nodes in China are undercounted, so they consider this a low estimate. Lots of factors will reduce the total number of clients seen, so I would consider this a minimum number of unique clients. Its a big network!
Most interesting to me is how many clients are on the most recent versions, and how many are running an unreleased version. Also, there are a lot of IPv6 clients, which is interesting for that unrelated adoption. Basically, I think this is cool data and I hope we get more, regularly.