First Photoshop, Then the Web
It's back into Photoshop or ImageReady to prepare the file for the Web. For example, you could include different states or provinces for rollovers. I added British Columbia, as shown in Figure 9. It's simple just to add a map containing all the states and provinces as a backdrop, and then trace around the region of your choice. When you fill the area, just remember to check Preserve Transparency. And, of course, make a copy of the layer you're changing so you have an original and a rollover version.
Figure 9 The map with British Columbia highlighted for a rollover.
It's best to work with the map in a larger format and then resize it for the Web. Optimizing this image is easy because it contains few colors. It will reduce in size nicely to a 32-color GIF image. Create any slices you may require; then export the image. Pretty painless, really.