relatedTags.rb

time = Time.now
tags = {}
Tag.order(count: :desc).limit(250).each do |tag|
  tags[tag.name] = Tag.related(tag.name).collect(&:name)
end
tags.to_json
(Time.now - time).to_s # time passed in seconds - ~8-11 seconds, potentially longer without caching

Using https://github.com/publiclab/plots2/blob/8a02ff48453c9397815c62aa764fde0b79bf88c6/app/models/tag.rb#L318-L319