Andy Kirk has just written about the latest project by Google's Big Picture Group, titled Music Timeline. It combines traditional stacked area graphs with stream graphs. The project is worth a visit, so I recommend that you spend some time exploring it. It's informative and fun. Don't forget to click on the FAQ button on the upper right corner to learn about the methodology they used (I'd like to know why this isn't a bit more detailed, and why the graphics don't have a scale, but anyway---)
That said, let me explain how I tried to navigate the graphic. First, I saw this:
I like Rock music, so I clicked on the dark green area. I got this:
Then, I clicked on the large section at the bottom, also labeled as Rock. This was the result:
Finally, I clicked on AC/DC, to get a sense of how the popularity of the band has changed throughout the years. I was disappointed. I couldn't really see anything here, as the baseline of the segment that I selected is constantly shifting, a problem all stream graphs share:
This connects to the main message in my latest long-form article, The Many-Faced Infographic. When designing an interactive visualization, why wouldn't you give readers the opportunity to explore the data in different ways? Just to give you an example of what I mean, visit this classic interactive graphic by The New York Times (2009):
Click on any area and see what happens: Suddenly, the segment you selected moves down to the zero baseline, making the task of seeing change across time much easier:
And, going back to the first screenshot from the Music Timeline, shown above, why don't you let me switch between the current area graph and a line chart in which all lines share a common zero baseline? That'd facilitate comparisons between genres. Just my two cents.