I did not know that. Thanks for the tip. My project is more of an experiment and for personal exploration and all that. So I don't mind if it has a strong competitor.
You can have a look at http://code.google.com/p/closure-library/. What I did downloaded the files and peeked through all of them. Closure has not been very popular with the community, but is currently running all google applications such as Gmail.
Also, there are many other Javascript visualization libraries besides the Google Chart API that you might want to know about (if you did't). All of them are open and can be locally run.
Indeed. Be careful with Protovis -- there hasn't been any work on it since last August or so, and the primary maintainer has pretty clearly moved onto D3.
If you're starting a new project, or even have some work invested in Protovis, I'd migrate it to D3. Working with a dead library isn't the best idea.
You can write your code in Processing or JavaScript, which is nice if you want to take advantage of the Processing library without having to learn a specific language.
One of the major gripes I had when I played around with the Google charts API is that it didn't seem to support log scales. Implement that and I'm sure you'll have won the hearts of a lot of frustrated developers. Looks great otherwise.
You can definitely use log scales with google charts, just it won't do it for you. You'll have to perform the math beforehand and send custom number labels.
A big advantage of CANVAS is to display charts on Android phones. Most of today's Google charts use SVG that, for some obscure reasons, can't be displayed on these devices out of the box.
"The use of SVG on the web is still limited by the lack of support in older versions of Internet Explorer (IE) which (as of December 2010) is the most widely-used browser. The most widely deployed version of IE (version 8) does not support SVG.[46][47] However, IE9 (released March 14, 2011) does support the basic SVG feature set.[48]"
and:
"Internet Explorer, up to and including IE8, was the only major browser not to provide native SVG support. Native support became partially available in IE9 (the current version of IE, as of March 2011),[48] including embedding SVG-file into HTML using “object” tag as well as “img” tag. IE8 and older require a plug-in to render SVG content."
All the routines are public, there is no need to go through the API.