Graphs & Diagrams : Text Equivalents : Common Issues

Alternative text for graphs

Complex images such as graphs, diagrams or illustrations, may convey a lot of information visually. It may be difficult to succinctly state all of that information in an alt attribute.

The simple solution is to describe all the information in the content text and then use a short alt text.

Another solution is to have a separate HTML page which contains a full description of the image. This may be linked to by an longdesc attribute:


            <img src="graph1.gif" width="300" height="300" longdesc="graph1.html" alt="graph 1" />

Browser support is sketchy for this attribute and the W3C suggest the use of a d-link instead.
A d-link is a standard text link using the letter "D" next to the image:


            <img src="graph2.gif" width="300" height="300" alt="graph 2" />

            <a href="graph2.html">D</a>

Graph example 1

Graph depicting the increase in internet usage between 1990 and 2005

What would make good body text to go alongside the graph?

The graph image and the alt attribute depicts all the required information.
As you can see from the graph Internet usage has increased dramatically over the years.
Internet usage has increased dramatically over the years with over 15 million users to date.
Internet usage increased dramatically over time. 1 million users between 1990 and 1995, 5 million between 1995 and 2000, and 15 million from 2000 to 2005.
None. The description required would be superfluous in the body text therefore it would be best to use either a longdesc attribute or a d-link.

Graph example 2

Graph depicting a small amount of Titanium alloy mixed into a large amount of Rhobundium

What would make good body text to go alongside the graph?

The graph image and the alt attribute depicts all the required information.
The smallest amount of Titanium is all that the alloy requires. Approximately 5 micrograms of Titanium is enough to mix with a kilo of Rhobundium.
The Rhobundium-Titanium alloy is relatively cheap to produce owing to the minimal amount of Titanium required.
Of all the alloys obtainable from the metals in the periodic table the Rhobundium Titanium alloy makes use of the dramatically different atomic weights.
None. The description required would be superfluous in the body text therefore it would be best to use either a longdesc attribute or a d-link.

prototype developed for:NGfL Accessibility Workshop 2004

2.01.09 Text equivalents: Graphs & diagrams

Alternative text for graphs

Graph example 1

Graph example 2