This was a great example of design hindering interpretation. The graph’s diagonal/diamond shape made legibility much harder. A traditionally oriented graph would have been trivial to read and correlation more obvious.
I didn't really understand how they came up with that as a trend line.
I agree that they made an obvious decision to give design preference over legibility. My first glance at the page was "this is neat", but as I tried to wrap my brain around the data, my thoughts changed to "what an unnecessary mess".
[1] http://2oqz471sa19h3vbwa53m33yj.wpengine.netdna-cdn.com/wp-c...
[2] http://www.visualcapitalist.com/relationship-money-happiness...