Start with the question the chart answers
Before choosing colors or chart types, write down what a reader should learn. Is the chart comparing groups, showing change over time, or revealing a range of values? That purpose should guide the title, labels, data table, and summary. A title such as “Monthly library visits, January through June” tells readers more than “Visitor trends.” It identifies both the measure and the period without asking them to interpret the graphic first.
Imagine a line chart showing visits to a neighborhood library over six months. A reader looking at the lines may quickly notice that visits rose in spring. Someone using a screen reader, enlarging the page, or viewing it on a narrow phone screen needs a route to the same information. An accessible chart offers several routes: readable labels on the graphic, the values in a table, and a sentence or two about the pattern. None has to carry the whole explanation alone.
Make labels do more than a legend can
Label axes with both the measure and its unit, such as “Visits per month,” rather than “Visits.” If an axis starts above zero or uses an unusual scale, say so plainly; otherwise, the visual difference between values can be misleading. Use category names that make sense outside the chart, and keep abbreviations to a minimum. A reader should not have to search elsewhere on the page to decode the basic terms.
When possible, place series names near the lines or bars they identify. Direct labels reduce the need to look back and forth between marks and a distant legend. If a legend is necessary, use the same clear wording in the legend and the data table. Do not rely on color alone to distinguish series: patterns, shapes, line styles, or direct labels can help people who cannot easily tell the colors apart. Check that text remains legible when the chart is enlarged or viewed at a smaller screen width.
Labels should also avoid making the picture crowded. If every data point cannot be labeled clearly, label the important points and provide the complete values in a table. The goal is not to fit every explanation inside the image; it is to make the chart understandable through the page as a whole.
Provide the underlying numbers in a usable table
A data table lets readers inspect exact values rather than estimate them from the height of a bar or the position of a point. For the library example, a simple table might have a “Month” column and a “Visits” column, with one row for each month. If the chart compares two branches, give each branch its own clearly named column. Use the same units and time periods in the chart and table so readers can move between them without guessing.
Keep the table as straightforward as the data allows. Column headings should describe the values beneath them, and the reading order should be logical. Avoid putting several unrelated measures into one cell or using color as the only way to identify a value. A table placed near the chart is easier to find than one hidden elsewhere on the site. It also remains useful when a chart image fails to load or is difficult to read.
The table is not merely a transcript of visual marks. It serves readers who want to compare exact figures, reuse a value, or check whether the written takeaway matches the data. If the chart shows estimates or rounded numbers, identify them as such in both places.
Write a summary that explains the pattern
A written summary should state the main observation, not just announce that a chart exists. For example: “Library visits increased from January to May, then declined slightly in June; May had the highest total.” If an exact value is central to the point, include it. For a more complex chart, mention a meaningful comparison or exception, then direct readers to the table for the full set of numbers.
Separate what the chart shows from why it might have happened. A rise in visits does not, by itself, prove that a new program caused it. Phrases such as “visits rose after the program began” describe timing without claiming a cause the chart cannot establish. This distinction makes the summary more useful to every reader.
Finally, consider how the chart is published. If it is an image, give it concise alternative text that identifies its subject and main takeaway, and keep the fuller table and summary nearby. If it is interactive, make sure its controls have understandable names and can be used without a mouse. Review the page as a complete experience: a reader should be able to understand the point, find the numbers, and tell what each value means without depending on sight or color alone.
