Beyond Basic Alt Text – Charts, Maps, and Diagrams

Bar chart of Digital Accessibility Lawsuits by year: 2016-262, 2017-814, 2018-2314, 2019-2890, 2020-3550, 2021-4195 (projected)

What is Alt Text?

Alt-text is one of the most basic elements of web and document accessibility.  For people who cannot see images contained within a website or document, a text alternative describing most images is required. However, not all images require alt text descriptions.  Repetitive logos and decorative elements such as watermarks can be artifacted and not given alt text. Learning to provide useful alt text is a skill that can take some practice. 

How do you know what to write?

When writing alt text, always keep in mind that “understandable” is one of the pillars of WCAG philosophy. Text alternatives should be concise, accurate, and relevant.  Read the text surrounding an included image to see how much additional information is actually conveyed by the image versus already present in the text.  The relevance of the image within the document informs how the alt text is written. 

portrait of Abraham Lincoln

For example, this image of Abraham Lincoln that hangs in the White House might have different alt text if it is contained in an article about paintings in the 19th century, versus an article about White House history, or an article about Abraham Lincoln himself. In the first, you might mention the painting techniques, in the second you might include where in the White House this painting can be found, and in the last, you might just say “Painting of Abraham Lincoln by George Healy 1869.”  It’s important to always be aware of the context for which the image has been included.

It’s complicated

Some images and graphics are extremely complicated and difficult to describe concisely while still providing relevant information. Elements such as pie charts, line graphs, organizational charts, maps, and flow charts can require hundreds or even thousands of words to describe them.  This is often necessary in order to supply a text alternative that provides the same information being provided by the image.  

Unlike regular text,  alt text cannot be broken into paragraphs or contain headings, This means lengthy alt text descriptions can be very difficult to use. If there is a 1,500-word description of a chart or graph, an assistive technology user who wants to double-check a fact part-way through may have to reread the ENTIRE alt text to find what they need.  There are, however, alternative ways to present the same data that may not require such a lengthy description. 

A picture is worth 1,000 words…

For most PDF remediation solutions, there are limits to how alt text for complex images can be provided.  Equidox software allows for some different options in adding alt text to images.  

Charts & Graphs

Usually, the absolute best alt text for any chart or graph is something like: “Chart showing an upward trend over time; refer to the data table on this page for specific details.”  If possible,  include the source data table for any chart or graph within the source document. If that isn’t possible, depending on the complexity of the chart, either general trends should be described, or each data point should be described in the alt text. Consider the intended context of the graph when determining how much detail to include.  

This graph can be described relatively simply.  “Line graph showing an upward trend in cell phone services from 2001 through 2010, with a corresponding downward trend in residential phone services over the same period.”

Simple Line Graph

For this particular bar graph below, however; it is necessary to provide the various data points in order to convey the information.  So you would write something like: “Graph of favorite cereals by vote.  Life  6 votes, Cornflakes  4 votes, Kix  3 votes, Cheerios  2 votes.”  Notice that these figures have been arranged in descending order.  This allows for an easier understanding of the trends.  It would be of more importance if there were a list of more items on which to vote, but this method of arranging in descending (or ascending) order should be used unless the graph has other sequential structure to consider (such as dates).  It is easier for assistive technology users who have visual or cognitive disabilities to understand the data being presented. That way if the user needs to quickly find the highest or lowest value, it is much easier than re-reading every item again. Note also that “votes” has been spelled out each time. This avoids confusion about what the various numbers are referencing.  

Example Bar Graph

For more complex graphs, Equidox allows users to create custom elements within PDFs that do not alter the visual appearance of the document.  The image can be tagged with alt text which refers to an additional zone that has been added to provide a less cumbersome alternative to lengthy alt text.

For example, if you do not have a data table available for a graph, it is possible to create one that assistive technology users can read, but will be hidden from visual users of the document. 

Equidox allows users to create a table zone to describe this image. Example complex line graph

So for this particular graph, the table might have dates as row headings, the various payment plans as column headers, and the data points can be filled in for each of the various cells.   The added table below would allow assistive technology users to get a full understanding of the graphed information.  Alt text for the image of the graph would refer to this table zone (“Graph of trends for Demo Video, by Payment Plan.  Refer to the data table which follows.”) The table would be included immediately after the graph image in the reading order.

Watch Demo Video by Payment Plan

Date Free  Startup Growth  Enterprise
Oct 5 125 75 25 20
Oct 6 175 140 100 25
Oct 7 202 177 172 41
Oct 8 200 205 210 55
Oct 9 275 245 205 90
Oct 10 375 290 185 100
Oct 11 400 300 105 120
Oct 12 360 320 100 165
Oct 13 345 375 90 195
Oct 14 300 350 75 205


Maps can be extremely difficult to describe accurately using alt text.  Often the alt text used is simply “map of…” This is not especially useful for an assistive technology user who might actually want to know how to get from point A to Point B or the location of a specific destination.   However, if the information conveyed by the map (directions or specifically cited locations like mailboxes or coffee shops) is thoroughly covered in the text of the document, the alt text “map of mailbox locations” might be perfectly appropriate.

Be cautious of using N, S, E, and W directions when describing a map unless the top of the map is actually facing north; otherwise, your directions may be inaccurate.  Sometimes referring to GPS coordinates (if available) can be helpful as many assistive technology users make use of the GPS on their smartphone to navigate their environment.  

Equidox custom elements can sometimes be used to describe a map.  Various sections of the map can be broken into smaller graphics by adding graphic zones and describing each area individually.  Very clean city block-type maps can sometimes be described in table form.  The strategy is to evaluate the map and its purpose and try to convey the information as accurately and functionally as possible.  

Remember the context of the map needs to be considered. It’s not always necessary to describe the entire map. The map below could take hundreds of words to describe in the alt text. 

Example map of the 2021 Baltimore Half Marathon Route

However,  the best way to provide the intended information for this particular map is to give clear directions to each point listed on the map.  So, you might write:

“Map of the course for the 2021 Baltimore Half Marathon. Start at the intersection of Pratt and Light streets.  Make the second right onto Baltimore Street. Turn right at the fifth intersection at Patterson Park.  Then take the next left onto Eastern Avenue and proceed one block.  Turn left onto Linwood Avenue.…”  and so on, describing the path of the marathon.  This is the information intended by the map.  Again, if the text around this map already includes step-by-step directions, it is not necessary to reiterate them in the alt text.  “Map of Route for 2021 Baltimore half marathon” will suffice. 

Organizational Charts

Organizational charts are another tricky element to describe using alt text.  The more complex the org chart, the more words are required to accurately present the information.  It can become very cumbersome to navigate alt text describing an organizational chart if there are a large number of elements.  

Equidox provides a unique solution because it can create zones that will be digital tags on export.  Many organizational charts can be depicted using a nested list.  Simply create a list zone and use custom text to enter the elements of the org chart and voila – easy to parse information for an assistive technology user.  The alt text for the org chart will then refer to the added nested list zone for the necessary information. The nested list should immediately follow the org chart image in the reading order. Here’s an example:

Example Organizational Chart

This organizational chart would be complex to describe as alt text.  However, it can be rendered in Equidox as a nested list, like so:

  • Board
    • General Manager
      • Human Resource Manager
        • Trainers
        • Recruiting Team
      • Design Manager
        • Design Supervisor
        • Development Supervisor
      • Operations Manager
        • Statistics Department
        • Logistics Department
      • Marketing Manager
        • Overseas Sales Manager
        • Service Department Manager

Flow charts

Flow charts can consist of many elements requiring a lengthy description as alt text.  The more interconnected the elements of the flow chart, the more lengthy the description.  One solution Equidox allows is the creation of multiple graphic zones over the entire image to represent each element.  Each of these graphic zones can be described individually, including their relationship to other elements.  As a last step, carefully set the reading order for these added graphic elements so the entire chart makes sense to the assistive technology user.

This chart can be easily described using regular alt text without the risk of it being too long.  However, each item can also be given its own graphic zone in Equidox, with each zone describing its relationship to the others.  

Example Flow Chart

You can provide separate alt text for “Start” (“Start”), “Look for lost item” (“Look for lost item”), “Did you find it” (“Did you find it, if not, continue to next step”), “Do you need it?” (“Do you need it, if so return to Look for Lost item.”) The additional graphic zones would also need to be labeled with the correct reading order.  

What about Hybrid Technologies?

Some assistive technology users with low vision may use hybrid technologies such as ZOOMText Fusion, a solution that zooms in on the page and also functions as a screen reader.  When using this technology, the user is seeing what is on the page greatly zoomed while hearing the digital tags read aloud by the screen reader. The use of this kind of hybrid technology may mean that some of these invisible PDF tags may be confusing.  If the zoomed visual area isn’t focused on the same part of the graph that the screen reader happens to be reading, the information may not be conveyed as cleanly.  You may wish to add a custom text field informing hybrid technology users that you’ve added tags to facilitate screen reader use. 

Concise, accurate, relevant, and in context

When writing alt text, always consider the context of the image and why it’s important to the specific document in which it’s located.  It sometimes requires a fair bit of creativity to convey the information in the most usable way.  Consider how difficult it will be for an assistive technology user to read through complex alt text and keep it simple by conveying only necessary, relevant information. 

Get inventive about how to make the information in the document’s images function as value-added rather than just more text to read.  Strive to simplify and break down complex images. Also, remember the “understandable” pillar of WCAG philosophy and keep it top of mind when adding alt text.  Equidox provides a few alternatives to just filling in the alt text box, and some of these options can reduce the need to bombard an assistive technology user with a wall of text to describe included images.  

Contact us to learn other ways that Equidox software can make your PDF remediation faster and easier and provide greater usability to end-users.

Check out this article for more on writing alt text: Can Image Recognition by Artificial Intelligence Replace Alt Text?


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Tammy Albee

Tammy Albee | Content Marketer | Onix Tammy joined Onix after four years experience working at the National Federation of the Blind. She firmly maintains that accessibility is about reaching everyone, regardless of ability, and boosting your market share in the process. "Nobody should be barred from accessing information. It's what drives our modern society."