How to Create Accessible Graphics

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Client-side versus server-side image maps

Two technologies exist for creating image maps: client-side and server-side.  The difference between the two technologies is found in the way the map is processed to determine which page should be loaded when the user clicks on the image.  Server-side image maps are an older technology that is not used much except for specialized applications.  When a user clicks on a server-side image map, the coordinates of the mouse position are sent to the server where they are processed by a program.  The program determines if the click is near a link position.  If it is, the server then sends back the linked page.  Because all the link information and processing is on server, there is no way to provide alternative text for server-side image map links.  If you are using server-side image maps, you should provide redundant text links that will be accessible to screen readers and other text only browsers.

Client-side image maps are newer and much more accessible.  The information for this type of image map is sent in the HTML source code of the page.  When a user clicks on the image map, the browser looks up the coordinates on the page and sends the user to the corresponding page.  Because the information is stored in the page, you can add alternative text for each of the hot spot regions of the map.

Fortunately, HTML editors create client-side image maps so if you are using an editor such as Frontpage or Dreamweaver the map you create will be a client-side image map.

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