[CALUG] Web design question

[Edward D. Browne]

Are there any of you web designers who can tell me something about
web sites such as this one:

http://www.nytimes.com/ref/us/politics/08RESULTS_SENANALYSIS.html

I think that's an excellent graphical display of  information, but I
don't know
enough about web design to understand how it's done.   I guess it's using
tooltips  to show details when you mouse over a county, but I've never
seen anything like the way it automatically displays the mouse-over details
from the corresponding county from the *other* election.  How is that
done?  And how do you create the graphical maps from (presumably)
the tabular data of the election results?  Are there commercial products
that do this, or reference books that explain it?

Thanks very much - Ed