Style.org’s Jonathan Corum’s has another informative entry on creating Edward Tufte style “sparklines” using the free Google Charts API. Sparklines are “little data lines” that show “active quality over time … small, high-resolution graphics embeeded in a context of words, numbers, images. Sparklines are data-intense, design simple, word-sized graphics” (Tufte).
The Google Charts API allows chart images to be created using standard URL encoded text data values when requesting the image source as the internet browser renders the page. You aren’t asking for a prebuildt chart image. Rather, Google is generating one on-the-fly customized for you with the specified parameters.