What TanStack Charts does for scatterplots on its own, and what you add so that everyone can read them.
What you get
A named chart. ariaLabel is required, and the chart is exposed as an image with that name. ariaDescription adds a longer description.
Keyboard navigation, on by default. Tab moves into the chart and focuses the first point. Arrow keys move between them, and Home and End jump to the first and the last. Enter or Space pins a sticky tooltip, and Escape closes it.
The tooltip is announced to screen readers as it changes, so a keyboard user hears the values of the focused point.
A visible focus ring in the theme's focus color, shown for keyboard focus only.
Reduced motion. Animated charts skip their animation when the reader has asked for less motion.
An interactive legend made of real buttons, each with a pressed state, when you use interactiveColorLegend.
What you add
A label that says what the chart shows, its unit and its period. "Car power against fuel economy, 1970 to 1982" works. "Scatter plot" does not.
A visible title, and a subtitle with the unit and the period, in HTML next to the chart.
The exact values another way, when they matter: a table under the chart, behind a toggle, or a download.
A second signal besides color for every series or part.
A keyboard path for every control you add yourself, such as a series filter or a period picker.
Name and describe the chart
Keep the label short and put the takeaway in the description. Do not put every value into the name: a screen reader reads it in one breath.
<Chart
definition={definition}
ariaLabel="Car power against fuel economy, 1970 to 1982"
ariaDescription="Fuel economy falls as power rises, and the most powerful cars use the most fuel."
/>
Give the values as a table
A table is the most reliable way to give exact values to everyone, including people who zoom far in or print the page. Render the same array the chart reads with the kit's Table, under the chart or behind a "Show as table" switch. When the values are only an illustration, a one sentence summary is enough.
Do not rely on color
Label each group next to its cluster, or split the groups into small multiples, so color is not the only way to tell them apart.
Label the few points that matter directly, so no one has to find them by color.
Draw the trend line in a color with strong contrast and a different width from the points, so it reads as a line in grayscale.
Marks need enough contrast with the background. Check light colors from a palette against the page in light and dark mode.
Many points
Arrow keys step through the points one at a time. With hundreds of points, that is a long way to the one a reader wants, and hearing every value does not give the pattern.
Put the takeaway in ariaDescription: the direction of the relationship, how strong it is, and any outliers.
Offer the rows as a table the reader can sort and filter, or as a download.
Add filters outside the chart, such as a group select, so fewer points are left to step through.
Bubble size
Size is hard to judge for everyone, and very small bubbles are hard to see. Keep a minimum radius of about 3px, and put the sized value in the tooltip and the table.
Turning the keyboard off
A static chart with no tooltip can pass keyboard: false in the second argument of defineChart, so it does not add a tab stop. Keep it on for any chart that shows values on hover: otherwise keyboard users never see them.
Check it
Tab into the chart and read every point with the arrow keys.
Listen to it with a screen reader.
Zoom the page to 400% and confirm the values are still there.
View it in grayscale and confirm the series are still apart.
The Accessibility guideline has the principles that apply to every chart.