[var_explained]

The first few graphs use the interactive [Stack Overflow Trends](http://insights.stackoverflow.com/trends) tool, which is all public data. This is useful since it lets readers modify the graphs (for example, to add a few more tags to the comparison).

The later graphs use data that's already not public (what tags users visit together, and what countries tags are visited from), so there's no reason not to use visits instead.

The graphs for visits over time do look very similar (in general question traffic by tag roughly matches questions asked, but as a slightly lagging indicator)