Guideline 5
Provide access to graphs for users who are blind or visually impaired.

Graphs are frequently used in math and science materials to present and summarize data. In visual form, they are not accessible to users who are visually impaired, although the data being graphed can be expressed in non-visual ways. Viable alternatives include generation of a tactile graph, delivering the information in text, interaction with an audio graph, or a combination tactile/audio approach. Consider using Scalable Vector Graphics (SVG) format for graphs, especially in HTML-based content. Accessibility features of SVG will permit improved viewing and printing of graphs as well as providing other benefits. SVG allows smooth enlargement of images to provide large, high quality graphs for users with low vision, and metadata included in SVG can be used programmatically to provide text information about graphs to blind users. For more information see:

Consider using Scalable Vector Graphics (SVG) format for images, especially in HTML-based content. Accessibility features of SVG permit improved viewing and printing of images. SVG allows smooth enlargement of images which can provide large, high quality images for users with low vision, and metadata included in SVG can be used programmatically to provide text information about images to blind users. For more information see:

Scalable Vector Graphics (SVG) 1.0 Specification
www.w3.org/TR/SVG

Accessibility Features in SVG
www.w3.org/1999/09/SVG-access

This guideline refers to all graphs including static graphs (provided as part of the instructional materials in a piece of software) and dynamic graphs (generated by the user as part of the product curriculum). Some techniques are only useful for static graphs.

Checkpoint 5.1
Allow all graphs to be printed.
Priority 1
Allowing graphs to be printed separately from an image of the entire screen is a simple and broadly useful adaptation with benefits similar to those of printing other kinds of still images, as discussed in Guideline 1. Using a printed graph, low vision users can create enlarged images. Blind users can print tactile graphs using specialized equipment. There are tactile graphics printers available that can print a graph and emboss any corresponding text in braille. Standard operating system drivers can create images and text of maximize usefulness. For example, send font and character information to the printer rather than images of text, because images cannot be converted to braille.

Checkpoint 5.2
Allow all graphs to be enlarged on screen.
Priority 1
A zooming or scaling feature, similar to one common in word processors, will improve access for users with low vision by allowing them to enlarge graphs to view smaller features. Ensure that lines and fonts are smooth and legible at the enlarged size.

Technique 5.2.1
Print graphs as scaled on screen
If enlarged graphs can be printed at that size, it is easier for blind users to convert on-screen graphs into tactile images as described in checkpoint 5.1.

Checkpoint 5.3
Allow users to control the width of lines and characteristics of fonts for viewing and printing graphs.
Priority 1
Some users can better read text and view graphs if they can adjust the thickness of lines and the size, color, and typeface of fonts. Allow these features to be customized within the product. Also, some operating systems allow users to set a default typeface and line thickness. Check the accessibility features of the operating system for which the software is being developed to see if there are default values which can be used throughout the software.

Checkpoint 5.4
Provide a complete description in text for static graphs.
Priority 1
In recordings of textbooks on audio tape for use by blind students, narrators routinely describe graphs and charts in words. A carefully scripted description can convey the main points of a graph. This text can be displayed on screen for use by assistive technology, delivered directly by the product with text-to-speech, or delivered programmatically through an accessibility API. See the section on access issues for selected development environments for information on accessibility APIs. The text should describe the layout of the graph, the location of variables on the graph, and the overall trend. Here is an example from the National Braille Association Tape Recording Manual (listed in Appendix 4, Guides to Spoken Mathematics):

Figure 5. 'The relationship between the vapor pressure of water and its temperature.' This is a line graph whose x axis is temperature in degrees centigrade, running from zero to one hundred degrees. The y axis is pressure in millimeters of mercury and runs from zero to 800 millimeters. The curve starts at the origin and rises so that when x is 25 degrees, y is approximately 40 millimeters. When x is 50, y is 100. When x is 75, y is just under 300. When x is 100, y is about 760. End of Figure 5."

Checkpoint 5.5
Provide summary information about dynamic graphs.
Priority 1
A dynamic graph probably has certain aspects, such as the range of the axes or the variables being graphed, which are known to the program. If so, this information is useful to blind users in determining which graph they are editing or printing. For example, if there is a user-editable graph, create a descriptive summary including the graph title, the names of any variables included in the graph, and the range of values for that variable. This text can be displayed on screen for use by assistive technology, delivered directly by the product with text-to-speech, or delivered programmatically through an accessibility API. See the section on access issues for selected development environments for information on accessibility APIs.

Checkpoint 5.6
Provide alternate formats for graphs.
Priority 1
Graphs presented in alternate formats provide more options for visually impaired users.

Technique 5.6.1
Provide tactile graphs for static graphs
One of the most thorough ways of conveying information contained in static graphs to people who are blind is to generate a professional quality tactile rendering of the graph. Consider creating a set of tactile graphics that represent the complete contents of the software. This set of tactile graphs can be made available either through the publisher's distribution mechanism or through an arrangement made with a tactile graph production facility. Availability of tactile graphs should be clearly documented in product help and in any appropriate teacher support materials that may accompany the software. There are several professional production facilities that have a wealth of experience producing tactile graphs. See Appendix 2 for a list of these organizations. Availability of graphics should also be listed with the American Printing House for the Blind, a central source of information on how educators can locate accessible materials, listed in Appendix 2.

Technique 5.6.2
Provide a brief orientation in text
While tactile graphs are helpful, many blind students find initial orientation to the graph difficult. A brief text explanation of the graph's layout will significantly improve students' ability to access and interpret the information conveyed on the graph. Teachers and students may also read the text to decide which graphs warrant more exploration. Text can be delivered within the software through an accessibility option or programmatically though an accessibility API, or could be included as a separate hard copy document shipped with the tactile graphs. This short orientation should give the title of the graph, the variables plotted on each axis, and their ranges.

Technique 5.6.3
Provide an audio equivalent to graphs
Through an innovative use of audio, software can provide interactive access to graphs using tones or text-to-speech. Since exploring values on static graphs and creating dynamic graphs is a real-time experience for other students, it should ideally be so for blind students as well. Creating audio graphs is not a fully developed field, but there are some examples to consider. The Triangle tool from the Science Access Project at Oregon State University provides audio access to graphs and tables; see dots.physics.orst.edu/triangle.html for more information.

Another approach is demonstrated in the CD-ROM Access Project's accessible prototype "Photosynthesis Explorer." This prototype can be downloaded from the Photosynthesis Explorer Prototype section. Here are some options for creating useful audio graphs.

Technique 5.6.3.1
Use tones to present an audio graph
Use an audio tone to illustrate rise and fall of a graph or the relative values of a variable in a pie chart. If a task requires that more than one variable must be tracked simultaneously or individually, each variable should be assigned a distinct voice, so that the rise and fall of the pitch indicates the change in value. Note that this option will not be useful for deaf-blind users.

Technique 5.6.3.2
Provide text output of a visual graph
Use text to deliver the numeric values in a graph interactively. The values can be delivered via text on screen to be read by a screen reader or through direct text-to-speech. More than one variable can be tracked in speech by including the variable name before each value and using different voices or pitches for text-to-speech. The CD-ROM Access Project's "Photosynthesis Explorer" prototype offers an example of how text output can be used to convey information normally accessed on a visual graph. This option will meet the needs of deaf-blind users if the text is displayed on screen or provided programmatically for compatibility with a screen reader.

Technique 5.6.3.3
Implement navigation features to allow users to explore data points while listening to a graph
Allow users to move through a graph at their own pace, using keyboard commands for navigation. At each increment, provide current graph values using text or tones or both. Allow students to play back the audio or text graph continuously then pause at a keystroke to confirm a numeric value for a particular point. Provide options to allow the user to configure this audio browsing experience for their needs.

Technique 5.6.4
Provide a haptic or haptic and audible means of obtaining information conveyed in a graph
Haptic technology allows one to tactilely experience a graph or 3D image through force feedback. Vision is the "highest bandwidth sense," so replacing the amount of information that can be perceived through vision with touch may require a multi-modal approach. Combining haptics with audio can create this richer sensory experience. Methods for providing haptic interfaces to scientific information are still undergoing research, however. For more information, consult these sources:

The University of Delaware's Information Access Laboratory
www.ee.udel.edu/InfoAccess/Technology/haptic.html

The University of Toronto's Adaptive Technology Resource
Centre www.utoronto.ca/atrc/rd/vrml/main.html