Hi. I have a project where users can search for participants by state and county. They start with a U.S. map, click on a state, then get a map of all the counties for that state, then click on a county to get all the participants in that county.

I have all of the coordinates for the U.S. map and the individual state maps stored in a database so that only those states and counties with participants in them are clickable. That is, the hyperlinks with map coordinates only appear if there are participants. It's a very dynamic site so I need this whole process to be very automated.

Here's my problem, though. In the early going, the vast majority of counties (and states, for that matter) don't have any participants, so the user is required to mouse over the map looking for counties in which there are participants. There's no immediate visual clue. Kind of clumsy. Is there a way to use CSS, for example, to use the map coordinates to shade a state or county? In other words, since the hyperlink/coordinates only appear for states and counties where there are participants, can I somehow take advantage of that fact to dynamically color the state/county using CSS or some other means? Or even just put some sort of small icon superimposed over the appropriate county/state on the map?

It would be easy to use a simple list or drop-down menu, but unfortunately that doesn't meet my client's requirements. Thanks in advance for any help.