Popularity determined by some form of "active users". e.g. users who have made at least 1 post in the past year. The exact metric will be determined by what sites choose to report and what can reasonably be estimated.

If a site is renamed, this resolves to the old name. If two sites merge, this resolves to the name of the new one if it kept an old name, or to the one that was bigger prior to the merge if not.

If you'd like a new site added, ask me and I'll add it. (You'll need to managram me M$25.)