How an Image Map Works

An image map has three elements; an image, a set of map coordinates, and an HTML host entry. The image can be any web graphic, usually saved as a GIF or JPEG. The map data set is a description of the mapped regions within the image. The host entry is HTML code that positions the image within the Web page and designates the image as having map functionality.

There are two main types of image maps, server-side and client-side; how the map data is stored and interpreted depends on the type of map. The regions in a map include shape descriptors (rectangle, circle, or polygon), numeric data defining the coverage of the regions within the image, and link URLs. Maps also include a layer order defining which regions take precedence when overlap occurs. An image map is positioned in a Web page using one of several image map variations of the 'IMG HTML' tag.

A downside to using image maps is that some people surf the web with 'image loading' turned off - this effectively speeds up their browsing but any images will not appear. To avoid any problems with navigation, text links would need to be included; the use of the 'ALT' attribute would suffice as it provides a text alternative for browsers unable to view the graphic.