Images maps allow you to specify multiple clickable regions in an image, each which take the user to a different URL. This is useful in any circumstance where you want to "drill down" to other information from an image - for example to the states of a state diagram, information about individuals in a photograph, or locations in a map, etc.
A simple example is provided below. The example links to the Help:Images page if clicked in a rectangular region in its centre or to the image itself when the blue "i" icon is clicked. In any other region, a click takes the user to the Main Page.
Error: Image is invalid or non-existent.
<imagemap> Image:Example2.png|150px|alt=Alt text rect 80 70 160 140 [[Help:Images|Link to Help:Images]] default [[Main Page|Go to main page]] </imagemap>
Regions can be specified in terms of rectangles, circles or arbitrary polygons (note that the co-ordinate system used to specify a mapped region is based on the original image dimensions).
The full syntax is described in the Extension:ImageMap plugin documentation.