Image maps enable you to link one or more areas of an image—called hotspots—to a URL. When a user clicks on the hotspot, the web browser loads the linked file.
The main difference between using image maps and using slices to create links is in how the artwork is exported as a web page. Using image maps keeps the artwork intact as a single image file, while using slices causes the artwork to be divided into separate files. Another difference between image maps and slices is that image maps enable you to link polygonal or rectangular areas in your artwork, while slices enable you to link only rectangular areas. If you need to link only rectangular areas, using slices may be preferable to using an image map.