CSS Tutorial : Image maps

Image maps enable you to define multiple links within a single image; for example, if you
have a weather map, you could use an image map to link to each region’s weather forecast;
or if you had a picture of your office, you could use an image map to make each of
the objects clickable, leading to pages explaining more about each of them. Clickable
regions within image maps can be fairly basic—rectangles or circles—or complex polygonal
shapes. Note that there are both server-side and client-side versions of image maps—
server-side image maps are now considered obsolete and pose accessibility problems, and
even client-side image maps tend to be avoided by most designers, although use of alt text
can help them become reasonably accessible.
Regardless of the complexity of the image and the defined
regions, the method of creating an image map remains the
same. To the right is the image used in this section to show
how a basic image map is created. It contains three geometric
shapes that will be turned into clickable hot-spots.
The image is added to the web page in the usual way (and
within a block element, since img is an inline element), but
with the addition of a usemap attribute, whose value must be
preceded by a hash sign (#).

<div id="wrapper">
<img src="image-map-image.gif" alt="Shapes" width="398" height="398"
å usemap="#shapes" />
</div>
The value of the usemap attribute must correlate with the name and id values of the associated
map element. Note that the name attribute is required for backward compatibility,
whereas the id attribute is mandatory.
<map id="shapes" name="shapes">
</map>
The map element acts as a container for specifications regarding the map’s active areas,
which are added as area elements.
<map id="shapes" name="shapes">
<area title="Access the squares page." shape="rect"
å coords="29,27,173,171" href="square.html" alt="A square" />
<area title="Access the circles page" shape="circle"
å coords="295,175,81" href="circle.html" alt="A circle" />
<area title="Access the triangles page" shape="poly"
å coords="177,231,269,369,84,369" href="triangle.html"
å alt="A triangle" />
</map>
Each of the preceding area elements has a shape attribute that corresponds to the
intended active link area:
rect defines a rectangular area; the coords (coordinates) attribute contains two
pairs that define the top-left and bottom-right corners of the rectangle in terms of
pixel values (which you either take from your original image or guess, should you
have amazing pixel-perfect vision).
circle is used to define a circular area; of the three values within the coords
attribute, the first two define the horizontal and vertical position of the circle’s
center, and the third defines the radius.
poly enables you to define as many coordinate pairs as you wish, which allows you
to define active areas for complex and irregular shapes—in the previous code
block, there are three pairs, each of which defines a corner of the triangle.
Creating image maps is a notoriously tedious process, and it’s one of the few occasions
when I advise using a visual web design tool, if you have one handy, which can be used to
drag out hot-spots. However, take care not to overlap defined regions—this is easy to do,
and it can cause problems with regard to each link’s active area. If you don’t have such a
tool handy, you’ll have to measure out the coordinates in a graphics package.

**Note:  that some browsers will place a border around the image used for an
image map. This can be removed by using CSS to set the image’s border to 0
(either via applying a class to the image, or via a contextual selector).