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In HTML and XHTML, an image map is a list of coordinates relating to a specific image, created in order to hyperlink areas of the image to various destinations (as opposed to a normal image link, in which the entire area of the image links to a single destination). For example, a map of the world may have each country hyperlinked to further information about that country. The intention of an image map is to provide an easy way of linking various parts of an image without dividing the image into separate image files.
The type of image map developed by Hughes is known as a server side image map, as the processing and link resolution happens on the server. This is accomplished by using an HTML forms input tag to contain the image. The default behavior of image buttons is to send the X/Y coordinates of the user's click back to a CGI process on the server. For an image map, this process consults a file located on the server to determine which URL these coordinates refer to, and redirects the browser to that location. Server side image maps have been largely replaced by client side image maps, which were introduced in HTML 3.2 and do not require executing separate processes on the server.
In HTML an imagemap is made of the actual image, that is embedded with the <img>-Tag. The image gets simultaneously the attribute usemap.
Following code defines a rectangular area (9,372,66,397) with a link to the English Wikipedia:
<img src="image.png" alt="image alternative text" usemap="#mapname" /> <map name="mapname"> <area shape="rect" coords="9,372,66,397" href="http://en.wikipedia.org/" alt="area alternative text" title="hover text" /> </map>
It is possible to create image maps by hand using a text editor, but doing so requires web designers to know how to code HTML as well as how to enumerate the coordinates of the areas they wish to place over the image. As a result, most image maps coded by hand are simple polygons.
Because creating image maps in a text editor requires much time and effort, many applications have been designed to allow web designers to create image maps quickly and easily, much as they would create shapes in a vector graphics editor. Examples of these applications are Adobe's Dreamweaver or KImageMapEditor (for KDE), and the imagemap plugin found in GIMP.
Image maps which do not make their clickable areas obvious risk subjecting the user to mystery meat navigation. Even when they do, where they lead may not be obvious. This can be partially remedied with rollover effects.