Image maps are used for images where you can click on different parts to go to different pages. Nowadays, this is usually handled in the browser, by client-side image maps. But it is also possible to do this in the server. This is done through .map files, where you define which page the user should be brought to when clicking somewhere on the image.

The HTML code needed to use an image map is:

<a href=file.map>
  <img src=image.gif ismap>
</a>

(X1,Y1)-(X2,Y2) URL

(X1, Y1) are the coordinates of the upper left corner of a rectangular area whose lower right corner has the coordinates (X2, Y2). Any point inside the rectangle will take the user to the URL.

(X,Y),R URL

Any point inside the circle centered at (X,Y) and with the radius R will take the user to the URL.

(X,Y) URL

This specifies a single point and ties a URL to it. If more than one point is specified in the file, the one closest to the position on which the user clicks will be used.

ppm: path

Use the PPM file referred to by path. Each color in that file may give a different URL.

pgm: path

As PPM, but the file is a grey scale file.

color:(r,g,b):URL

In all PPM files referenced, this color will point to the URL. r,g and b are decimal integers between 0 and 255 and the color defined is the combination of the red (r), green (g) and blue (b) intensities. If the file searched is a grey scale PGM file, the grey scale will be (r+g+b)/3.

color:(r,g,b)-(r,g,b):URL

All colors in the range will point to URL. If the file searched is a PGM (grey scale) picture, the grey scale will be (r+g+b)/3.

color:greyscale-greyscale:URL

All colors with an intensity falling within the range will point to URL.

default:URL

The url URL will be returned if nothing else matched. Don't forget to set it.

void:URL

The url URL will be returned if the client doesn't support image maps or if the map file is accessed without coordinates.