Standard: Charts (pie, bar, line, etc. - not tables)
Brief description
(see the full document below for details)
Charts are often the best way to display large amounts of data in a form that can be quickly compared and understood. Use this type of graphic appropriately and be sure to comply with section 508 requirements.
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Content requirements
- Use charts to present large amounts of data in a compact, visual format. Charts are best at showing patterns, not individual data points.
- Present four or fewer data points in text rather than in a chart or graph.
- Provide the source for the information presented in charts, maps and graphs whenever possible.
- Do not display information in 3-D.
- Do not rely solely on color to differentiate the data. Note that Section 508 requires that "Web pages shall be designed so that all information conveyed with color is also available without color, for example from context or markup."
- Avoid using acronyms on maps, graphs and charts
- Spell out units of measurement. For example, spell out million metric tonnes of carbon dioxide emissions rather than using the acronym MMTCO2E. If there isn't room on the image itself, include an acronym legend beneath the graphic.
- When presenting charts that cannot be read at small screen sizes, either:
- present a large version of a map, graph or chart on the page (keeping the file size as small as possible) with no text wrapping or
- present a smaller, potentially illegible version (thumbnail) of the graphic, with a "view larger version of image" link beneath it that takes visitors to a pop-up window or new page that displays a larger version of the graphic
- Ensure that your maps, charts and graphs comply with section 508 by providing equivalent information to visually-impaired visitors. Options include:
- Provide the text equivalent of the information:
- in the alt text for the graphic,
- elsewhere on the page, or
- on a separate page that the viewer can access by clicking on the graphic (see the Examples section below).
- Provide in the alt text an alternative source for detailed information, such as a phone number that the viewer can call to receive further information about the contents of the graphic.
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Examples
This chart uses large bars and units that can be read easily, spells out the unit "MMTCO2E" in a legend, and provides the data source:
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Rationale
Charts must be easy to understand and legible.
Avoid 3-D graphics because they are difficult to interpret. Pie chart sections are distorted depending on where they appear in the pie and horizontal lines on bar charts don't necessarily match the vertical scale depending on where they are in the 3-D "box."
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Related governance documents
EPA
Related Policies
Related Procedures
Related Standards
Related Guidance
Non-EPA
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Full Metadata about this standard
Name Charts (pie, bar, line, etc. - not tables)
Tracking number NT00000000
Type Standard
Required or Recommended Required
Effective date 09/28/2005
Date approved 09/28/2005
Category Graphics and Multimedia
Web Council review by 09/05/2008 (or earlier if deemed necessary by the Web Council)
Governing Policy Web Governance and Management (PDF) (4 pp, 339K, About PDF)
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