Are you talking about drawing 20,000+ elements as arc segments on one circle? No, that can't really be what you mean -- there would never be that many pixels to draw them all distinctly.

Anyway, the previous reply takes care of drawing the arc segments without having them overlap each other (using the "-start" attribute together with the "-extent"), and with that, assigning a tag to each segment so that you can identify one that is clicked on.

Note that when assigning colors to arc segments, you may need to alternate light and dark shades (and reserve a "medium" shade in case you have to draw an odd number of segments) -- otherwise, it might be hard to see where the segment boundaries are.