[pak]

Canvas tiles are exactly the approach we took in making the ChromoZoom genome browser, where we wanted people to smoothly zoom in on client drawn data at 60fps through 10 orders of magnitude: http://chromozoom.org (Note that it's only used for user provided data, as the default tracks are prerendered, like Google maps v1.)

I highly recommend this hybrid approach of 10-20 canvases plus a sprinkling of HTML elements for anybody looking to maximize responsiveness in this type of UI. In our tests, SVG and HTML start stuttering in draggable layers around tens of thousands of elements (easier to hit than you'd think). We actually decided to do mouseover calculations ourselves, in a pixel map within a mousemove handler, since having separate elements to trigger the mouseover was too expensive.