In the last section, we made an explanatory graphic that used interaction to guide the user through the data. Often, however, the goal is just to make a dataset interactive and give the user some way of manipulating it, in other words, an exploratory graphic.
D3's behaviors save a boatload of time setting up the more complex interactions in a chart. Additionally, they're designed to handle differences in input devices, so you only have to implement a behavior once to have it work with both a mouse and touch device. The two currently supported behaviors are drag and zoom, which will get you pretty far.
Instead of having the user click buttons in the last example, what if we just let them drag the chart area to see the UK's prison population change? It involves a bit more work on the user's behalf, but it also gives them the ability to freely navigate through the chart, which may be desirable in some circumstances.
Let's extend our prisonChart object again. Comment out everything...