Important, yes, but. How about the breakdown of drug users vs. drug dealERs who are in prison? Is there a difference between the categorization of users vs dealers? I'm not trying to say that the racial breakdown seems disproportionate, but this chart is not quite comparing apples to apples. (edited to fix a typo, which is in CAPS).

roughly 4/5ths of arrests are for possession vs sales: http://www.bjs.gov/content/dcf/enforce.cfm

And whites are slightly more likely to be sellers than blacks (4th paragraph): http://www.washingtonpost.com/blogs/wonkblog/wp/2014/09/30/white-people-are-more-likely-to-deal-drugs-but-black-people-are-more-likely-to-get-arrested-for-it/

@sfrazer thanks!

Now, those additions add context and make the chart make more sense. I'll mark these articles to read later. Thank you sfrazer.