An imagemap is a "clickable" image that HTTP-compatible browsers treat as a special case: Clicking in different areas on the picture causes different URL's to be loaded. Graphical menus, clickable building maps, and clickable blueprints are some of the many possible applications of imagemaps.
Only two files are required for image mapping, both in any directory: a .map file, and an actual image file. The .map file contains a list of coordinates to define the regions of the map that cause the different effects when clicked in. The imagemap is entirely specified by the .map file. There are 3 different methods to specify the regions that can be clicked in: They can be specified by circles, they can be specified by polygons, or by simple rectangles. Although each has the same basic structure...

method url coord_1 coord_2 ... coord_n
...each one uses the coordinates in a slightly different way. The coordinates are specified simply by listing an x,y pair. Here's how to specify the region types: Remember, the url is the url you want to be associated with the specified region. It can be a partial URL as well as a full URL (you can reference index.html instead of http://your.server.dom/current_directory/index.html). Also remember, you can use "#" as the first character in a line to specify a comment.
Once you have the .map file set up, you can put the image map into action. It can be referenced by the following structure in HTML:

<A HREF="myimage.map"><IMG SRC="myimage.gif" ISMAP></A>

The map file specifies the anchor, and the image file specifies the image to be displayed and clicked upon. Here is a sample .map file. We have an image, say "bign.gif" which we want to make clickable. We have a circle, a rectangle, and a polygon in the shape of an N.


# bign.map:  Sample imagemap definition

# the circle around the logo
circle http://home.netscape.com/circle.html 25,25 0,25

# a rectangle inside the circle
rect http://home.netscape.com/rect.html 0,0 15,30

# the n in the middle
poly http://home.netscape.com/n.html 15,35 15,10 25,15 35,10 35,35 15,35

# anything else
default http://home.netscape.com/tryagain.html

Then the image is referenced by:

<A HREF="bign.map"><IMG SRC="bign.gif" ISMAP></A>