TIP 76

Use Client Side Image Maps

Client side image maps shall be provided instead of server-side image maps except where the regions cannot be defined with an available geometric shape.

Explanation

An image map is an image that has "active regions". When the user selects one of the regions, some action takes place -- a link may be followed, information may be sent to a server, etc. To make an image map accessible, content developers must ensure that each action associated with a visual region may be activated without a pointing device.

Image maps are created with the MAP element. HTML allows two types of image maps: client-side (the user's browser processes a URI) and server-side (the server processes click coordinates). For all image maps, content developers must supply a text equivalent. As with other links, the link text should make sense when read out of context.

Content developers should create client-side image maps (with "usemap") rather than server-side image maps (with "ismap") because server-side image maps require a specific input device. With client-side image maps, each "active region" in a picture can be assigned its own link that specifies what web page to retrieve when a portion of the picture is selected. By contrast, clicking on a location of a server-side image map only specifies the coordinates within the image when the mouse was depressed - which link or URL is ultimately selected must be deciphered by the computer serving the web page.

Client side image maps are preferred over server-side image maps for at least two reasons: they are accessible to people browsing with non-graphical user agents and they offer immediate feedback as to whether or not the pointer is over an active region.

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