Before we get into the nitty gritties of how data can be made to persist between pages, I think it would be a good idea to give a concrete example of why one would want to implement such a thing. As a practical example, imagine you’re writing a Web site for your small rock band. You haven’t made it big yet, but you have a cult following that would like to be able to receive notices of your upcoming gigs. On your Web site, you want to create a form for people who would like to sign up to your mailing list, and you want people to be able to confirm their e-mail address before sending it off to you.

This article about persistent data will be a little different from the first two. The first article, which covered javascript mouseovers, and the second, which covered frames, explored techniques that can easily be taken and applied to just about any website out there. In contrast, this article is a little more abstract, presenting a technique that, while extremely useful when needed, is not likely to be added to just any website.

An image map is an image that comprises different clickable areas. Each area is a link that when clicked takes the visitor to a different URL. For example, imagine a map of the world, where each country takes the visitor to a web page about that country when clicked. In HTML speak, each clickable area is actually a hyperlink. Image maps provide an easy way of linking various parts of an image without dividing the image into separate image files.