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Image mapsThe IMG element can also be used to set up image maps, a more sophisticated form of clickable image, in which different effects can be achieved by clicking on different parts of the image. An example might be a map of a geographical region including several towns, where clicking on a particular town brings up information specific to that town. An image map is designated by the inclusion of the ISMAP attribute in the IMG element:
<A HREF="link-url"><IMG SRC=image-url" ISMAP></A>
The coordinates of the point on the image where the user clicks are
sent to the server, along with the URL specified in the anchor. An
external image map processing program is usually started by the Web
server to perform a mapping from the coordinates to another hypertext
document. There are standard programs, distributed with the CERN and
NCSA servers, that will handle fixed mappings according to
specifications stored in configuration files. If you want anything
more complex, such as mapping to dynamically generated documents, you
generally need a bespoke program (see Chapter The server may need to be configured to deal with the coordinate data. This depends on which image map processing software, if any, is installed on the server. The CERN htimage program allows contributors to set up their own image maps and associated files, without the need for intervention on the part of the server administrator. The NCSA imagemap program requires that all image maps be registered in a central configuration file, which is normally coordinated by the server administrator.
A type of image map can also be included in fill-out forms, using an
INPUT element of type IMAGE. This is discussed in
Chapter
![]() ![]() ![]() ![]() ![]() Next: Creating image maps Up: The IMG element Previous: Images as hypertext
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