December 12, 2003

Night of the Image Map

by Stuart Robertson

Published in: CSS, HTML and XHTML, User Interface Design |
Discussion is closed.

In the old days, before we thought much about web standards or the importance of accessibility, web designers used image maps to quickly divide a single image into regions, and link those regions to separate URLs. Traditional image maps, though, don’t work well with text-only browsers, and they aren’t as efficient or versatile as many newer techniques. You might still find them in use on an old web page or perhaps some kind of complex map, but most web designers would consider it an old technique. A dead one.

While collaborating on a horror fiction web project, I decided early on that I’d do my best to code the site using only standards-based XHTML and CSS. When the other designer sent me his concept for the site, I began to despair. He wanted the page to look like an old weathered book, with rough edges and grungy textures. The menu items were scattered about the page. How could I turn a well-structured document into something that looked so organic?

I thought about image maps.

They were horribly outdated, but an image map would make things so much easier than chopping the background image into dozens of pieces and trying to use CSS to stitch it back together. It might have been crazy to think about using them again, but the the old ways seemed to hold the answer. I decided to go back into the laboratory and see if I could use the modern science of CSS to bring this web design technique back to life...

These are the facts as we know them

To make our image map, we’ll use CSS to create invisible links and float them over the background image wherever we need them to be.

First we create an outer div which will be used to apply the background image. Our links will go inside a nested div to keep our code organized and allow us to apply styles to the links as a group. The nested div can also come in handy when using a style sheet switcher to create alternate CSS menu effects.

<div id="book">
 <div id="menu">
  ...
 </div>
</div>

The individual links can now be placed inside our nested div. Giving each link its own id allows us to independently position them on the page. These separate ids also act as anchors, letting users select the links directly no matter where they are located on the page, or their ability to click on them.

To make the text within each link invisible, we need to add another nested tag. I prefer to use semantically meaningless <i> tags because they provide visual clues to their presence in the absence of a stylesheet, which makes them easier to work with. They’re also very short, which helps with code efficiency. However, you could certainly use <span>, <em>, or some other tag if you’d like. {Line wraps are marked ». –Ed.}

<div id="book"> 
 <div id="menu"> 
  <a href="index.html" id="home"><i>Home</i></a>
  <a href="preface.html" id="preface"><i>Preface</i></a>
  <a href="stories.html" id="stories"><i>Stories</i></a>
  <a href="galleries.html" id="gallery"><i>Galleries»
  </i></a>
  <a href="forums.html" id="forum"><i>Forum</i></a>
  <a href="mementos.html" id="mementos"><i>Mementos»
  </i></a>
  <a href="credits.html" id="credits"><i>Credits</i></a>
  <a href="indicia.html" id="indicia"><i>Indicia</i></a>
 </div>
</div>

This is the all the XHTML that we need. You can see the results in Example 1. We can now move on to creating the image map effect with our stylesheet.

Guided by a master plan

In your CSS file add a background color for the document body and set the margin and padding to 0. We’re going to be using absolute positioning, and this will help with our calculations.

body {
  background-color: #000;
  margin: 0;
  padding: 0;
  }

The background for our image map is applied to the outer div. You should set an appropriate height and width to make sure it is fully displayed.

#book { 
  background-image: url(/d/imagemap/images/»
   bookpages.jpg);
  height: 595px;
  width: 750px;
  }

Any styles that apply to the majority of the links can be defined together. More specific CSS rules can then be used to alter the attributes of individual links as required. Use absolute positioning and include a default height, width, and top position for all of the links. This is a good time to make sure the underlines are removed as well.

#menu a {
  position: absolute;
  height: 38px;
  width: 88px;
  top: 31px; 
  text-decoration: none;
  }

To hide the text within links while retaining “clickability,” we use a CSS selector to identify the italicized text within the links contained in our nested div, and its visibility is set to hidden. It’s important to include meaningful link text, even if it will be invisible to the majority of your users. This ensures that your site will be accessible for browsers that don’t support CSS and users who are viewing it with an alternate stylesheet.

#menu a i { visibility: hidden; }

Once the general CSS is in place, we can position each link individually. To improve efficiency, links that share a common attribute such as left or top, can be defined together.

a#credits, a#indicia { top: 531px; }
a#home { left: 101px; }
a#preface { left: 221px; }
a#stories { left: 311px; }
a#gallery { left: 431px; }
a#forum { left: 526px; width: 61px; }
a#mementos { left: 591px; width: 98px; }
a#credits { left: 431px; }
a#indicia { left: 591px; }

When applied to the XHTML of our document, the menu links will now float independently above our background image. If we position them above areas of the image that look like links, we’ll be all set. Placing your links correctly will usually take either careful calculation or a bit of trial and error.

CSS image maps can use the :hover pseudo element to define a separate style for for each link’s rollover state. This allows us to float new images above the background whenever the user moves their mouse over one of the invisible link areas.

a#home:hover { background-image: url(/d/imagemap/»
   images/homeglow.jpg); }
a#preface:hover { background-image: url(/d/imagemap/»
   images/prefaceglow.jpg); }
a#stories:hover { background-image: url(/d/imagemap/»
   images/storiesglow.jpg); }
a#gallery:hover { background-image: url(/d/imagemap/»
   images/galleryglow.jpg); }
a#forum:hover { background-image: url(/d/imagemap/»
   images/forumglow.jpg); }
a#mementos:hover { background-image: url(/d/imagemap/»
   images/mementosglow.jpg); }
a#credits:hover { background-image: url(/d/imagemap/»
   images/creditsglow.jpg); }
a#indicia:hover { background-image: url(/d/imagemap/»
   images/indiciaglow.jpg); }

A bug in Internet Explorer that causes the rollover images to refrain from disappearing as expected can be fixed by adding border: none to the :hover state of all the CSS image map links.

a#home:hover,
a#preface:hover, 
a#stories:hover, 
a#gallery:hover, 
a#forum:hover,   
a#mementos:hover, 
a#credits:hover, 
a#indicia:hover { border: none; }

You can see the final results of our CSS image map in Example 2.

Post mortem

Using large background images isn’t bandwidth-friendly, but it can produce compelling designs and give high-bandwidth visitors a richer visual experience. Because CSS image maps use standards-based XHTML, we could use a style sheet switcher to offer a low-bandwidth, alternate view of the site.

Special thanks to Nate Piekos and Shane Clark for their work on Dead Ends, Massachusetts, where the image map and other dark things were brought back from the grave.