There are many good resources that provide more information about spending from the G20. Here are a few more places to check out:
While these data sources contained most of the information in this website, some spending values were imputed. For example, China does not publish nominal education statistics, but it does share its education spending as a percentage of its GDP. In cases where data was missing, average values or linear extrapolation was used.
The charts used in this website were designed using the Google Charts API. You can read more about them here.
Styling and functional aspects of the site were written under the jQuery and Bootstrap JavaScript libraries. Special shoutout to W# Schools for providing an endless stream of web design examples.