CREATING A CLICKABLE IMAGE MAP

Image maps explained

Image maps can be either client-side or server side.

An image map is a way of defining "hot spot" links within an image on a Web page. This means that, rather than having
the whole image behave as one link, you can have lots of different links within the one image.

Example: on the map below each parish is a hot spot, when clicked on,
takes you to a infomation page about that particular parish

To turn an image into an image map simply add the usemap attribute to the img tag for the image.

Like:
< img src="images/graphic.jpg" width="375"
height="102" style="border: none;" usemap="#xxxxx"/>
Where usemap="#xxxxx" associates the image map with the image.

Creating an image map with the map tag:

The other part of the process is the map definition itself. In this definition, you tell the browser where the hot spots
are in the image, and what the hot spots need to link to.

The map is defined using the < map> < /map> tag.

An example with the map tag looks like this:

< map name="shapes" id="shapes">

< area shape="circle" coords="58,50,40"
href="javascript:clicked_on('circle');"
title="Circle" alt="Circle"/>

< area shape="rect" coords="136,11,227,89"
href="javascript:clicked_on('rectangle');"
title="Rectangle" alt="Rectangle"/>

< area shape="poly" coords="309,13,358,89,257,89"
href="javascript:clicked_on('triangle');"
title="Triangle" alt="Triangle"/>

< area shape="default"
nohref="nohref"
title="Default" alt="Default"/>

< /map>

In the above, there are three (3) "hot spot" areas in the image map a circle, a rectangle, and a polygon and
each of these areas is linked to a JavaScript function to display the appropriate shape name.

The above map element is placed AFTER the image in the HTML file.
In fact, it can be placed anywhere within the HTML page body.

The general syntax for the map element is:

< map name="map-name">

< area shape="area shape" coords="area coordinates"
href="area hyperlink" or nohref="nohref"
target="hyperlink target"
title="area title" alt="alternate text"/>

< area shape="area shape" ...

< /map>

So, each image map is given a name (map-name), and one or more area tags to specify the hot spots in the image.

The area tag has the following attributes:

shape="rect | circle | poly | default"

Specifies the shape of the area. Possible values are:

* rect (a rectangular shape),
* circle (a circular shape),
* poly (an arbitrary polygon, with 3 or more points), or
* default (which represents the remaining area of the image not defined by any area tags).

coords="area-coordinates"

Specifies the coordinates that define the corners of the shape. The coordinates depend on the shape specified in the shape attribute:
Shape Coordinates
rect coords="x1,y1,x2,y2"
(The top left and bottom right corners of the rectangle)
circle coords="x,y,r"
(The centre and radius of the circle)
poly coords="x1,y1,x2,y2,x3,y3,..."
(The corners of the polygon)

Note that all coordinate values are relative to the top left corner of the image. In other words, the top left corner always has coordinates (0,0).

Note also that the default shape type does not need any coordinates.

href="area-hyperlink"

This is the URL that you'd like to link the hot spot to. It works just like a standard < a href=...> tag.

You can specify a nohref attribute instead, in which case the hot spot will not link to anything.

target="hyperlink-target"

This is the optional target window or frame to open the linked URL in. Again, it works just like the target attribute in a standard < a href=...> tag.

title="area-title"

This attribute allows you to give the area a title. When the mouse is rolled over this hot spot, the browser will usually pop up a tool tip displaying this title.

Putting the image map in a separate file

The name of the image map specified in the usemap attribute is really a URI, which means it can reference a map in another file on your website, if required.

For example, if you saved your map element in a file called xxxxx.map in the same directory as your HTML file, you would reference the map using:

< img src="images/xxxx.jpg" width="375" height="102" style="border: none;" alt="xxxxx" usemap="shapes.map#xxxxx"/>

Server-side image maps

As an alternative to defining the whole image map in HTML for the browser to read, you can use server-side image maps. With this type of map, the browser simply sends the (x,y) coordinates of the point clicked on to a server-side script (such as a CGI script).

To define a server-side map, you simply include the ismap attribute, and place an < a href> tag around the image, specifying the server-side script to send the (x,y) information to:

< a href="shapemap.cgi">
< img src="images/xxxx.jpg" width="375"
height="102" style="border: none;" ismap="ismap"/>


Then, when you click on the image, the browser sends the (x,y) coordinate of the point that you clicked on to the server-side script, which can then interpret these (x,y) values and take an appropriate action. The coordinates are appended as parameters to the end of the script URL:

Server-side image map data flow diagram

For example, if you wanted the user to choose a country from a world map image, you could use the server-side script to calculate which country was clicked on, and then display information about that country.

Another way of creating a server-side image map is with the image input type in web forms:


src="images/shapes.jpg" width="375"
height="102" style="border: none;"/>


In this case, the (x,y) coordinates are sent as form fields named fieldname.x and fieldname.y. So in the above example, the coordinates would be contained in the fields shapes_image.x and shapes_image.y. It's best to use a server-side map whenever the map has many areas, or where the areas are not easily defined by simple shapes such as circles, rectangles and polygons.

Working out image map coordinates

If you're using a Web page editor such as Macromedia's Dreamweaver you can draw image maps straight onto your images and let the editor work out the coordinates, but what if you're editing your page by hand?

One easy way to work out coordinates is to change your image map from client-side to server-side temporarily, by changing the usemap="mapname" attribute to ismap="ismap", and adding a dummy < a href> tag around the image, e.g.:

< a href="#"> < img src="images/shapes.jpg" width="375"
height="102" style="border: none;" alt="Shapes" ismap="ismap"/>

Then, as you roll the mouse over the image, you should see the coordinates appear after the "?" in the status bar of your browser! Try moving your mouse over the image below to see if this works:

If you can't get that working, another technique is to open your image in a graphics package such as Adobe Photoshop. You can then move the mouse over the image and see the mouse coordinates in the Info Palette.