This exercise will help you develop your skills in writing meaningful alt texts for digital images containing data visualisations.

Alternative texts are textual image descriptions that can be read out loud by assistive technologies such as screen readers, but also machine-read by, for instance, search engines. An alt text may help convey the purpose and main message of a visualisation to readers who are blind or have impaired vision or cognition.

Because an alt text is typically very short it is difficult to include all aspects that you might want to communicate. There are many ways in which you can compose an alt text, but in this example we are going to take a closer look at the following, very basic, "formula" for writing alt texts for data visualisations, as suggested by data visualisation designer Amy Cesal:

Alt = ”[Chart type] of [type of data] where [reason for including chart]”

In addition, she advises to include a link to the data source somewhere in the main text, so that a reader may access it using a software that they prefer.

Example

The chart below is designed by Maarten Lambrecht for the European Union's Data Visualisation Guide. Let's try and apply Amy's formula on this visual.

Line chart of EU's rising renewable energy use, averaging 23% in 2020. Highest use in Sweden (66%). Ireland lowest at 6%

Source: Maarten Lambrechts, CC BY 4.0.

[Chart type...] = The way in which the data is represented visually, in this case in the form of a line chart.
of [type of data] = The type of data that the chart is based on. Unfortunately, this line chart lacks horisontal and vertical axis legends; these elements could have provided us with some inspiration (instead, there is a title and a short subheading). This line chart appears to describe the share of renewables in energy used for heating and cooling in the EU, Sweden and Ireland from 2004 to 2020.
where [reason for including chart] = The main message and purpose of the visualisation. What might a viewer deduce from looking at this visualisation? The same visualisation can be used to tell many different stories. When writing an alt text, ask yourself what you want your readers to focus on and look for. For instance, this chart shows that the average proportion of renewable energy used in the EU is increasing. It has roughly doubled from 2005 to 2020, reaching 23.1 percent in 2020. Sweden has the highest share, with two thirds of its energy being of renewable origin. Ireland has the lowest share, with 6.3 percent of its energy coming from renewable sources.

You might need to customise an alt text and highlight different aspects of a visual depending on the context. Furthermore, there are often technical limits regarding how many characters you are allowed to use when publishing an alt text online. In our case, the maximum character limit in the learning platform used for this course is only 120 characters, which presents a significant challenge. Due to these limitations, this image was given a very condensed, general alt text when uploaded to the platform: ”Line chart of EU's rising renewable energy use, averaging 23% in 2020. Highest use in Sweden (66%). Ireland lowest at 6%”. Note that the creator of this chart has also used the title, "European Union slowly on its way to greener heating and cooling", to signal and reinforce the take-home message (in a somewhat subjective way, considering that the word slowly has also been added).

Exercise

Write your own version of an alt text for the line chart shown above, inspired by the formula ”[Chart type] of [type of data] where [reason for including chart]”.
Now, let's focus on a chart that you have created yourself. Your task is to summarise its main message with the help of Amy's formula.
- Start by asking your self this: What do I want my audience to look for?
- Then write an alt text using a maximum of 150 characters. (If you are writing your draft in for example Microsoft Word, you can use the "Word count" dialog box to see how many characters you have used).
- Then try to rewrite it into an even shorter version, using 120 characters or less.
- How did you change your text to make it more concise when you were only allowed to use 120 characters or less?
- How objective is your [reason for including chart], do you think?
The chart title is typically the very first thing a reader looks at. If your chart already has a title, take a moment to compare the message in your chart's alt text to that of your title. How might you improve the title, to better communicate your main message and make it easier for your readers to quickly understand what your chart is meant to illustrate? Is it possible to understand your main message by only reading your chart title and not looking at the chart at all?
Lastly, reflect on the possibilities and challenges of providing access to the raw data that your visualisation is based on. What might you need to consider when sharing data openly? Indeed, there are many ethical aspects and principles to take into consideration when sharing research data. There may be many reasons why you should not share your data.