line

Connects data points with a line. A line draws through a set of points, so it is most often paired with selectAll() to trace a layout produced by another chart. selectAll hands line an array of refs, and the line reads placed geometry off them.

from gofish import layer, chart, scatter, blank, selectAll, line

layer([
    chart(catch_locations)
        .flow(scatter(by="lake", x="x", y="y"))
        .mark(blank().name("points")),
    chart(selectAll("points")).mark(line()),
]).render(w=500, h=300, axes=True)

Signature

line(stroke=None, strokeWidth=None, opacity=None, curve=None) -> Mark

Parameters

Parameter	Type	Description
stroke	str	Line color
strokeWidth	int	Line width in pixels
opacity	float	Opacity, 0–1
curve	str | dict	Path shape; default "auto", which auto-smooths continuous line charts

Returns a Mark for use in .mark().

The line pattern

A line needs points to connect. The idiomatic recipe:

1. One chart positions invisible blank marks and names the layer with .name("points").
2. A second chart selects that layer — chart(selectAll("points")) — and draws a line() through it.
3. layer([...]) composes the two.

This separation lets the same positioned points back both a line and, say, circles drawn on top.

Sugar: .connect()

When the line connects a chart's own marks, skip the two-chart selectAll recipe and chain .connect() on the builder:

chart(data).flow(
    scatter(by="lake", x="x", y="y")
).mark(circle()).connect(line(stroke="steelblue", strokeWidth=2))

See .connect() for the full semantics; the explicit layer([...]) + selectAll form connects another chart's marks.

Examples

# Styled line
chart(selectAll("points")).mark(line(stroke="black", strokeWidth=2))