Explained here. Critiques in the comments are (mostly) valid, but for a first effort at using this kind of visualization technique, I'd say it's pretty impressive.
Effective but disturbingly silent - next time they should add a little elevator music.
Interesting how that was my first reaction as well - I kept upping my volume on the laptop, to no avail.
That was fascinating. It was clear that a lot of people in the comments didn't quite get what he was doing. This was an experiment in the technique, not a definitive historical essay.
His choice in calling his subject Maritime Empires confused me at first. My first thought was that it represented naval power. Overseas Empire is the English phrase that best represents what he meant.
There is plenty to nit-pick in the history. How did he pick certain dates? Where is Ireland? Why is Spain bigger than Britain at the end? I would love to see an historian take it over now and work on the details, add Germany, Italy, Japan, the Netherlands, Belgium, Denmark, and the US.