Why is this chart so damn hard to read?

My summer course on analytical methods is already at the midway point. I was doing some research on recommendation systems the other day, and came across the following chart:

Ouch. This is from the Park, et. al. (2012) survey of research papers on this subject. It's the 21st century, people. The column chart copies the older-generation Excel design made infamous by Tufte, and since abandoned. Looking more closely, I suspect that the chart was hand-crafted, not made in Excel.

There are several challenges of reading this chart.

The gaps between columns are narrower than the columns. Only in the last two years do the eight categories all count. So a key task is to learn which column stands for which type of application. Having one's eyes flip back and forth between the columns and the legend below the chart is a big hassle. As readers, we tend to learn a short cut, which is to memorize the order of the categories (first column is book, second column is document, etc.). The incorrect width of zero-valued columns thwarts this simple strategy.

The designer creates another obstacle by sorting the categories alphabetically. Shopping and movies are two of the most important applications and that message is buried.

The key to cleaning up this graphic is to bring the visual design closer to the question being addressed. The question of the chart is how interest in various applications has changed over time.

Here is a small-multiples presentation of the same data:

The answer is that applications are getting more diversified (the rise of the Other), and that Documents, Shopping and Movie applications were growing while research on Image, Music, TV Program and Book stagnated during the study period.