Server-side image maps track the exact coordinates where a user is pointing on an image. When the user clicks on a region in the map, only the map coordinates are sent back to the server. The server that generates the Web pages then has to calculate a response based on those coordinates. Since the coordinates are sent back over the Internet, alternative text (using ALT tags) cannot be used to provide accessibility because the user's computer is only aware of the coordinates, not the meaning assigned to those coordinates. Only the server-side computer that generates the Web pages can identify what those coordinates mean. Because alternative text cannot be used for server-side image maps, a separate listing of each of the "hotspots" of the map should be provided to ensure accessibility.
|Example of Proper use of Server-Side Image Map with Alternate links provided:
<IMG ISMAP SRC="imgmapcwa.gif" ALT="Please use the following links instead of this image map."></A><BR>
<a href="http://weather.noaa.gov/cgi-bin/iwszone?Sites=:ctz012">S. New London, CT</a> |
<a href="http://weather.noaa.gov/cgi-bin/iwszone?Sites=:ctz008">N. New London, CT</a> |
<a href="http://weather.noaa.gov/cgi-bin/iwszone?Sites=:ctz007">N. Middlesex, CT</a> |
A server-side image map - with text equivalent
S. New London | N. New London | N. Middlesex