A senior data scientist is developing a dashboard for a public-facing federal health agency report. A key visualization is a time-series line plot displaying the prevalence of five different virus variants over two years. The dashboard must comply with Web Content Accessibility Guidelines (WCAG) 2.1 AA standards. The initial design uses distinct colors to differentiate the five trend lines, which is insufficient for accessibility. To ensure all users, including those with color vision deficiencies and those using screen readers, can interpret the data accurately, which of the following represents the most comprehensive and effective strategy?
Convert the line chart into a series of five separate small multiple charts, one for each variant, to eliminate the issue of overlapping lines.
Combine a colorblind-safe palette with distinct dashing patterns for each line, and provide a properly tagged data table of the underlying data immediately following the chart for screen reader access.
Add ARIA tags to the chart's SVG elements and write a detailed long description (longdesc) attribute that summarizes the key trends and intersection points of the data series.
Replace the current color scheme with a high-contrast, sequential color palette and increase the line weight to improve general visibility for low-vision users.
The correct answer provides the most comprehensive strategy for making a complex line chart accessible. It addresses multiple accessibility needs simultaneously. Combining a colorblind-safe palette with distinct dashing patterns for each line ensures that users with various forms of color vision deficiency can distinguish the data series, adhering to WCAG 1.4.1 which prohibits using color as the sole means of conveying information. Providing a properly tagged data table is the most robust method to give screen reader users full access to the underlying data, allowing them to explore values independently, which is superior to a long text description.
The option to only use a high-contrast sequential palette is incorrect because it still relies solely on color to differentiate categories. The option to use ARIA tags and a long description is less effective than a data table for a complex chart, as navigating a long text description is more cumbersome for a screen reader user than exploring a structured table. Converting the plot to small multiples is a plausible visualization choice, but it fundamentally changes the chart's purpose from direct comparison to individual analysis, and it does not inherently solve the accessibility issue for screen reader users without an accompanying data table.
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