Google Charts is a combination of two application programming interfaces (APIs), Google Chart API and Google Visualization API. Google Chart API creates static visualizations of data and embeds them into webpages. Some HTML programming experience is recommended. Available visualization types include standard scatter, line, bar, pie, and box charts as well as Venn diagrams, dynamic icons or callouts, formulas, and connectivity graphs. In addition, maps can be made and embedded into webpages.
The Google Visualization API creates dynamic visualizations that allow for user interaction within a webpage. These visualizations are created with Java scripting, and Google provides links to Java script tutorials as well as source or example code in a Java library. In addition to the visualization types available with Google Charts API, Google Visualization API include timelines, heat maps, tree maps, word or term clouds, filters for other visualizations, and interactive Google Maps.
Data sources that can be used for both APIs include any file that can be imported as a two-dimensional table, including text files, spreadsheets, and database tables. The data must be retrieved using a retrieval protocol and the structured accordingly. Google provides Java, Python, and Google Web Toolkit (GWT) libraries for data retrieval, as well as an API to retrieve data from Google Spreadsheets.
For comparison of the two APIs: http://code.google.com/apis/charttools/docs/choosing.html