An image map adds one or more hyperlinked areas (or ‘hotspots’) to a single image.
Image maps are often used for geographic interfaces such as location guides.
Without using an image map, a separate image is required for each hyperlink. If creating a geographic interface, for example a tourist map of New Zealand regions, a separate image would be required for each region. The separate-image approach is of limited use as images have rectangular boundaries. Even if an image appears non-rectangular (through the use of transparency), the clickable area is still rectangular. Image map hotspots allow for more organic clickable-area shapes.
A single image with image map is faster to download than multiple, individually-hyperlinked images. This is due to the way the browser requests information from a server (using HTTP); for each image a new connection is made before the image is downloaded. Each image request connection adds to the overall time it takes for a webpage to load.
An image map require an image to be displayed before it can be used. If separate images are used instead, alternative (alt) text can be used to display a text equivalent in place of each image.