School of Professional Studies Office of Distance Learning

This page is related to Accessibility

At a Glance

Higher education often employs images that convey a dense amount of information. Maps, diagrams, flowcharts, graphs, and more—these are visualizations that allow sighted readers to take in a high amount of data or information very quickly. But blind and low-vision users may not be able to see these visual representations. Figuring out how to convey the information contained in complex images in text form can be tricky!

This guide, based on a presentation given by Dr. Valerie Morrison (Georgia Tech) for AHEAD in February 2021, breaks down specific considerations when writing alt text for complex images. The context of an image is critical to writing a good description.

Cognitive Load

A key concept to keep in mind when writing alt text for complex images is cognitive load. This refers to a person’s mental resources, especially working memory, when engaging with information. This is especially important when thinking about screen reader users and how they interact with alt text. Someone viewing a graph can glance around the image as much as they need to in order to refresh themselves on different data points.

But a screen reader user is listening to an audio version of that information—and depending on the screen reader, the user may not be able to rewind or replay the alt text with ease. This means that screen reader users may have to hold a lot of information in their working memory in order to understand the data. Most people can only hold about seven items in their working memory at once; more than that, and information is lost. (For individuals with cognitive disabilities, the amount might be considerably less.) Learning is improved when the number of items that have to be stored in working memory are reduced.

Writing Alt Text with Cognitive Load in Mind

Here are some general tips for writing alt text in a way that will reduce cognitive load.

• Simplify word choice and edit for clarity.
• Avoid redundancies with surrounding text, or write brief alt text directing users to information in a table or attached content page.
• Use parallel structure and clear, concise word choice.
• Spell out acronyms or abbreviations and explain what symbols stand for.
• Work from general to specific.
• Group similar items and describe relationships, and describe similarities first, then differences.
• Organize information in predictable, consistent ways.
• Focus on meaning rather than appearance.

Take the time to edit the alt text after you’ve written it. Return to it after a day and read through it to ensure that it is clear, precise, and easy to understand.

Complex Images

The following tips explain how to write good alt text for complex, data-rich images. It’s important to note that, in many cases, the alt text won’t be placed in the alt text field of the image; instead, it may be a table underneath the image or a linked content page with paragraphs of description.

Bar Graph

allixpeeke, CC0, via Wikimedia Commons

Work from general to specific. Begin with the type of graph and the name of the graph, then give the names of the horizontal and vertical axes. Then describe the data in as much detail as the course requires, which could be overall trends or specific numbers. The data could also be conveyed in a properly formatted, accessible table below the image for improved accessibility.

Line Graph

Andrew T. Levin, William P. Hanage, Nana Owusu-Boaitey, Kensington B. Cochran, Seamus P. Walsh & Gideon Meyerowitz-Katz, CC BY 4.0, via Wikimedia Commons

Include the title of the graph, the X and Y axes and ranges. Summarize line trends, such as Prediction Intervals, Confidence Interval, Meta-Regression slope, etc. If specific data points are needed, convert the information into a table.

Flowcharts

JulieJenksButteCollege, CC BY-SA 4.0, via Wikimedia Commons

Reproduce the information on a separate content page in a numbered or ordered (bulleted) list or use paragraphs with clearly labeled headings. In both cases, information about the structure or process depicted should be clearly stated (for example, “If Yes, proceed to Step 3. If No, proceed to Step 4″ or “There are three sub-types of Myeloid Stem Cells …”).

Complex Infographic or Diagram

KDS4444, CC BY-SA 4.0, via Wikimedia Commons

Begin with a general overview, such as the title or a high-level description of the information. Comprehensive information, such as a detailed walkthrough of the image, can be provided on a separate content page if needed for the course. Depending on the complexity of the image, one or more tables can be used to organize the data as well.

Maps

Cornell University Library, Public domain, via Wikimedia Commons

Describe the areas, regions, and relevant details on the map. You do not have to include every continent, country, region, province, or state shown, for example—only the ones relevant to the information students need to get from the map. In addition, be sure to describe any insets or zoomed-in areas of focus. Colors, shapes, and arrows can be left out of descriptions.

Timelines

Rubin Observatory/NSF/AURA, CC BY 4.0, via Wikimedia Commons

Begin by describing the range of the timeline and the type of events listed. For example, “Rubin Observatory Construction Time, 2011 to 2023 .” Then list events by date. If the timeline is fairly short (fewer than five items), this can be in the alt text field. Otherwise, consider a numbered list broken up by era (or whatever time frame makes the most sense). Any additional text information should be included as well.

Implied Visual Information

Creators may sometimes arrange or present the data to make a point visually. For example, in a graph showing military spending by country, structuring the graph so that the United States is at the top with a much larger bar than any other country is making a statement about the budget priorities of the United States. This implicit communication of information needs to be considered and conveyed in the alt text as well, but it’s important to still remain objective. Explain what the graphic is communicating and how, but don’t inject your own opinions or your assumptions about the creator’s opinions into the alt text.

Conclusion

Writing effective alt text for complex images requires careful attention to cognitive load, ensuring that descriptions are clear, concise, and structured to minimize memory strain for screen reader users. Strategies include simplifying language, organizing information logically, and focusing on meaning rather than appearance. For very complex visuals, detailed descriptions may be provided beyond simply using alt text, using tables or linked content pages to convey the full scope of the information.