The Pew Research Center has released a new report about political polarization in the U.S. The report includes an embeddable chart which combines animation and interaction quite effectively. NYT's The Upshot showcases it in its latest story. The challenge? It's hard to know what the chart is showing, as it isn't properly labeled —and it lacks a y-axis! I get that this a distribution/density plot or histogram, but it's not clear at all. How am I supposed to understand the data that the curves' height is representing? Is this kind of minimalism becoming trendy? Or am I missing anything here?
UPDATE: See these other charts, also by Pew. They do have y-axes.
UPDATE 2: The Pew folks have explained why they didn't include the y-axis. I get their point, but I'm still unconvinced. Both the area (areas, actually, as these are intervals) under the curve and the height of the segments matter. If you believe that most people may find histograms confusing, you can include a short explanation of how to read them. And if you fear that showing some very valuable context data —as they do in the little charts at the bottom of the post— "would overwhelm the visual impact of the changing distribution," why don't you make those numbers and tick marks visible just on demand? A little toggle (visible-invisible) button could work.