Accessibility

Accessible charts combine a clear visible title, a text description, readable contrast, and encodings that do not rely on color alone. SVG can carry this information as document structure for assistive technology.

from dataviz import Plot, save

def main() raises:
    var plot = (
        Plot()
        .mark_line()
        .encode(x=[1.0, 2.0, 3.0], y=[4.0, 7.0, 6.0])
        .labels(
            title="Weekly Orders",
            x_title="Week",
            y_title="Orders",
            description="Orders rise from four to seven, then fall to six.",
        )
    )
    save(plot, "orders.svg")

For SVG, save() turns the plot title and description into accessible document markup. Descriptions should communicate the takeaway, not enumerate every pixel. Check contrast in the final destination and use high_contrast() or print_safe() when appropriate. The default categorical palette uses Okabe-Ito colors, but color alone is still insufficient. For categorical series, combine shape, position, labels, or line patterns with color. See the named palettes.

Filled shapes have no marker or dash to fall back on, so Theme(fill_pattern_by_category=True) draws a pattern over each category’s fill: pie and donut slices, stacked and grouped bars, funnel steps, streamgraph bands, treemap and sunburst branches, marimekko cells, nightingale and polar bar wedges, and population pyramid sides. Each category’s HatchStyle is dealt by the same index as its color, legend swatches included, and the first category stays solid. The patterns are drawn as ordinary lines and dots, so PNG, SVG and PDF output match.

Colors and patterns are dealt by position, so a category’s look changes when the list does: after sort_categories(), or in a facet missing one series. fill_colors() and fill_patterns() pin them by name instead, and the legend follows. A pinned pattern is drawn even with fill_pattern_by_category off, which is how to mark one slice and leave the rest solid. Names a chart does not have are ignored, so one map can serve every panel of a figure.

See SVG accessibility, High-contrast theme, and accessible SVG helpers.