You've made it through the chapter on data!
Lastly, we made a cool map that showed a particular set of data, where we mashed up multiple datasets to create something cool. You'll find most of the more interesting data visualizations you build involve combining multiple datasets -- with your new-found skills with promises, you're well on your way to mashing up all the data.
In the next chapter, we'll look at making our stuff pop visually by adding animations. Now things are starting to get pretty exciting!