Next: Creating image maps Up: The IMG element Previous: Images as hypertext

Image maps

The 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 .

• Creating image maps for use with CERN and NCSA servers
• The mapedit program
• Specifying an image map in an HTML document
• Button bars: an image map application

Spinning the Web by Andrew Ford
© 1995 International Thomson Publishing
© 2002 Andrew Ford and Ford & Mason Ltd
Note: this HTML document was generated in December 1994 directly from the LaTeX source files using LaTeX2HTML. It was formatted into our standard page layout using the Template Toolkit. The document is mainly of historical interest as obviously many of the sites mentioned have long since disappeared.