The standard methods for doing imagemaps on the Web have traditionally involved a three step process:

1. The client clicks on a point on the image
2. The coordinates of the point clicked upon are sent to the server.
3. The coordinates are matched against a file containing the list of URLs and co-ordinates (called a "map" file), and the URL which is associated with those coordinates is returned to the client.

Step three sometimes involves running a script on the server. Because of the steps involved, imagemaps tend to be slower than normal hotlinks, and use up much more system resources on the server.

Client Side Imagemaps are imagemaps which do not have to make a separate call to the server to determine what URL should be returned to the browser. The coordinate/URL correlations are kept in the HTML coding of the page itself. After clicking on the image, a request for the correct URL is immediately sent to the server, just as when a normal hotlink is clicked. This method loads the page quicker, and uses less system resources in the process.

Another advantage of Client Side Imagemaps is that when the mouse pointer is held over sections of the map, the URL of the destination page shows in the browser (In Netscape it appears at the bottom of the window) instead of just coordinates.

The following is an example of a Client Side Imagemap:

If you view the source of this page you will see that this imagemap was created with the following tags:

<MAP NAME="MyMap">
<AREA SHAPE="rect" COORDS="1,114, 224,150" HREF="communications.html">
<AREA SHAPE="polygon" COORDS="10,15,99,4,105,24,77,57,23,54" HREF="web.html">
<AREA SHAPE="circle" COORDS="162,55,50" HREF="earth.html">
<AREA SHAPE=default HREF="none.html">
</MAP>

<IMG SRC="/graphics/webcomi.gif" USEMAP="#MyMap">