Alt text is a requirement that allows students with screen readers to get the full meaning of visuals. This can be straightforward with general photography or illustrations; in this resource, we offer tips for trickier visuals such as pie graphs, geometry diagrams and scatter plots.
Screen readers are a type of assistive technology used by people who are blind or have low vision, and are unable to read the content of graphs, charts or diagrams displayed as images. They can, however, read alternative text that summarises an image effectively. It’s important to write alt text to convey a detailed explanation of the data, trends and key insights presented in a graph to deem it accessible. For more complex images, an image description might be needed.
Use one of the following 3 methods to create a text-based alternative that can be read by a screen reader:
Very simple graphs, charts and diagrams can be summarised by using an alt-text description or providing the same data in list form on a linked page
More complex graphs and charts need to be represented in table form on the same page
Diagrams should be accompanied by a text description that explains the content, which:
ensures that the information can be accessed by both screen reader user
is relatively easy to implement
improves the accessibility for all students regardless of their access needs
Useful tip
Writing alt-text descriptions of complex material requires an understanding of the content and access to information about how to write effective alt-text descriptions to make them accurate.
Bar charts
Bar graphs should be converted into accessible tables
Briefly describe the graph and give a summary if one is immediately apparent
Provide the title and axis labels
It is not necessary to describe the visual attributes of the bars (e.g. dark blue, light blue), unless there is an explicit need such as an exam question referring to the colours
Provide the title and labels
It is not necessary to describe the visual attributes of the bars unless there is an explicit need
When working with double bar graphs:
explain the data on the x-axis and the y-axis and summarize the overall trend
List the data in bullet form
Use the appropriate vocabulary in context with the surrounding text depending upon depending on age/grade level (e.g. using the word ‘about’ and not ‘approximately’ for a lower grade level, and is consistent with surrounding text)
Although the bars on the chart reach approximate numbers, giving specific numbers makes it less wordy and more meaningful
Example of accessible bar graph
Alt text: Vertical bar graph. Refer to image description below.
Image description: Figure 1 is a bar graph that measures cheese consumption per capita in the top four cheese eating countries from 2017 to 2021. The consumption increases and decreases in different years. The data is summarized in the following table:
2017
2018
2019
2020
2021
France
52
58
60
58
69
Germany
53
53
55
53
62
Luxembourg
49
55
57
53
59
Iceland
47
54
55
53
69
Cheese consumption per capita (kilos) in the top 4 cheese eating countries.
Line graphs
Line graphs should be converted into accessible tables
Briefly describe the chart and give a summary if one is immediately apparent
Provide the title and axis labels
It is not necessary to describe the visual attributes of the lines (e.g. solid, dashed) unless there is an explicit need such as an exam question referring to these attributes; in the below case, with just two lines, the added description is not a burden to the reader
Example of an accessible line graph
Alt text: Line graph. Refer to image description below.
Image description: Figure 2 is entitled ‘Australian Cheese Trade’. There are two lines on the graph, a solid line labelled ‘Exports’ and a dotted line labelled Imports. The vertical axis is labelled ‘Millions of Dollars’, beginning with zero to seventy, in increments of 10. The horizontal axis is labelled ‘Year’ and lists all the years from 2013 through 2023. In the graph, the ‘Exports’ line begins in 2013 at 26 million dollars, rises steadily to 35 million in 2017, drops to 15 million in 2021 then rises to 34 million in 2022. In the graph, the ‘Imports’ line begins in 2013 at 44 million and rises steadily to 56 million in 2020, drops to 20 million in 2021, and then rises to 60 million in 2022. The data is summarised in the following table. Figures are in millions of dollars; all data is approximate.
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
Exports
26
27
25
25
26
29
35
30
15
34
Imports
44
46
49
51
52
53
53
56
20
60
Australian cheese trade ($m)
Pie graphs
Pie graphs should be converted into accessible tables
It is not necessary to describe the visual attributes of the charts (e.g. red wedge, blue lines) unless there is an explicit need such as an exam question referring to these attributes
It is helpful to list the numbers from smallest to largest, regardless of how they are presented in the image
Example of an accessible pie graph
Alt Text: Pie graph. Refer to image description below.
Image description: Figure 3 is a Pie Graph that shows the percentage of different fillings in a spanakopita.
SPanakopita fillings
percentage
Onions
4%
Eggs
6%
Ricotta
10%
Feta
35%
Spinach
45%
Fillings in a Spanakopita pie by percentage
Cartesian (X-Y) coordinates
State what type of graph is shown
Describe the x-and y-axes and what they represent
Write out the points in bullet form
Depending on how important the data points are to the central teaching point of the figure, the comma between the x- and y-coordinate may be written out as the word comma
Example of accessible X-Y coordinates
Alt Text: Cartesian (x-y) coordinates graph. Refer to image description below.
Image description: Figure 4 is a line graph with the x-axis labelled Cheese Volume (cm^3) and goes from 0 to 10. The y-axis is labelled Cheese Mass (g) and goes from 0 to 10. There is a formula stating slope equals to rise over run which equals to 2 grams divided by 2 cubic centimetre which gives you a slope of 1 gram per cubic centimetre. There are 7 data points plotted on the graph, which rises from left to right. The data points are (1,1), (3,3), (4,4), (6,6), (7,7), (9,9), and (10,10). From the point (4,4) to (6,6), the run equals 2 cubic centimetres and is 2 units to the right. The rise equals 2 grams and is 2 units up.
Geometry diagrams
Traditional descriptions of math diagrams benefit from descriptions that are brief and specific.
Organize the description in a linear fashion, for example moving left to right and use bullet points or line breaks to aid in navigation.
The description should focus on what is not included in the caption, i.e., points and lines.
Like any image, there are many effective ways to describe a math diagram and make sure you use short sentences that focus on the data.
Scatter Plots
Scatter plots are among the more difficult graphs to describe, especially if there is a need to make specific data point accessible
Provide the title and axis labels
Identify the image as a scatter plot and focus on the change of concentration
If it is necessary to be more specific, convert the data into an accessible table
Example of an accessible scatter plot
Alt Text: Scatter plot. Refer to image description below.
Image description: This is a scatter plot that shows the relationship between the stretch percentage and protein content in cheese. The x-axis is labelled Protein Content (%) and ranges from 5 to 35, in increments of 5. The y-axis is labelled Stretch Percentage (%) and ranges from 100 to 900, in increments of 100. There are approximately 15 data points plotted on the graph. Most of the data points are concentrated in the lower-left corner and diminish in concentration as the pattern extends toward the upper-right corner.
Protein content %
stretch percentage
20
400
15
350
30
600
25
450
18
300
22
250
12
255
28
700
10
200
24
550
8
150
32
800
14
240
26
600
16
350
Relationship between stretch percentage ang protein content table
Venn diagrams
Focus on the data in the Venn diagram, not on its appearance
Provide the data in brief statements
Give a summary if one is immediately apparent
Include the caption only if it is not accessible from elsewhere in the text; in this example, the caption is part of the image file and is therefore only accessible as part of the description
Example of Venn diagram
Alt Text: Venn diagram. Refer to image description below.
Image description: Venn diagram depicting the distribution of 100 individuals based on lactose intolerance and cheese consumption. The diagram consists of two overlapping circles. The left circle represents 20 lactose intolerant people, the right circle represents 40 people who eat cheese, and the overlapping area of the circles represents 40 people who eat cheese and are lactose intolerant.