That 30,000 figure, atheists are so enamoured of comes from the World Christian Encyclopaedia. It counts (for example) Catholics in England as being a different denomination than Catholics in Scotland, or Methodists in France as being a different denomination from Methodists in America.
Christians are usually accounted of as belonging to a different denomination if their theology, or practice, or both differs from that of another group. Living in different parts of the world, or even different parts of the same country, doesn't normally get them classified as belonging to different denominations. The WCE does it differently because it is basically a handbook for missionaries.