Line Chart with Arrows

This example shows a simple line chart with two types of arrow annotations. The Unicode character approach is simpler, while the line plus triangle point mark allows for greater flexibility, such as customizable arrowheads.

Method syntax

import altair as alt
import numpy as np
import pandas as pd


x = np.linspace(1,7)
data = pd.DataFrame({
    "x": x,
    "y": np.sin(x),
})

unicode_arrow_with_text = alt.layer(
    # Arrow
    alt.Chart().mark_text(size=60, align="left", baseline="bottom", fontWeight=100, angle=340).encode(
        x=alt.datum(2.8),
        y=alt.datum(-0.3),
        text=alt.datum("🠃")  # Any unicode symbol could be used instead
    ),
    # Text
    alt.Chart().mark_text(size=14, align="center", baseline="bottom").encode(
        x=alt.datum(1.8),
        y=alt.datum(-0.1),
        text=alt.datum("decreasing")
    )
)

mark_arrow_with_text = alt.layer(
    # Arrow line
    alt.Chart().mark_line(size=2).encode(
        x=alt.datum(5.4),
        y=alt.datum(-0.4),
        x2=alt.datum(5.9),
        y2=alt.datum(0)
    ),
    # Arrow head
    alt.Chart().mark_point(shape="triangle", filled=True, fillOpacity=1).encode(
        x=alt.datum(5.9),
        y=alt.datum(0),
        angle=alt.AngleValue(23),
        size=alt.SizeValue(100),
        color=alt.ColorValue("#000000")
    ),
    # Text
    alt.Chart().mark_text(size=14, align="center", baseline="bottom").encode(
        x=alt.datum(4.7),
        y=alt.datum(-0.3),
        text=alt.datum("increasing")
    ),
)

line_with_points = alt.Chart(data).mark_line(point=True).encode(
    x=alt.X("x"),
    y=alt.Y("y"),
)

line_with_points + unicode_arrow_with_text + mark_arrow_with_text

Attribute syntax

import altair as alt
import numpy as np
import pandas as pd


x = np.linspace(1,7)
data = pd.DataFrame({
    "x": x,
    "y": np.sin(x),
})

unicode_arrow_with_text = alt.layer(
    # Arrow
    alt.Chart().mark_text(size=60, align="left", baseline="bottom", fontWeight=100, angle=340).encode(
        x=alt.datum(2.8),
        y=alt.datum(-0.3),
        text=alt.datum("🠃")  # Any unicode symbol could be used instead
    ),
    # Text
    alt.Chart().mark_text(size=14, align="center", baseline="bottom").encode(
        x=alt.datum(1.8),
        y=alt.datum(-0.1),
        text=alt.datum("decreasing")
    )
)

mark_arrow_with_text = alt.layer(
    # Arrow line
    alt.Chart().mark_line(size=2).encode(
        x=alt.datum(5.4),
        y=alt.datum(-0.4),
        x2=alt.datum(5.9),
        y2=alt.datum(0)
    ),
    # Arrow head
    alt.Chart().mark_point(shape="triangle", filled=True, fillOpacity=1).encode(
        x=alt.datum(5.9),
        y=alt.datum(0),
        angle=alt.AngleValue(23),
        size=alt.SizeValue(100),
        color=alt.ColorValue("#000000")
    ),
    # Text
    alt.Chart().mark_text(size=14, align="center", baseline="bottom").encode(
        x=alt.datum(4.7),
        y=alt.datum(-0.3),
        text=alt.datum("increasing")
    ),
)

line_with_points = alt.Chart(data).mark_line(point=True).encode(
    x=alt.X("x"),
    y=alt.Y("y"),
)

line_with_points + unicode_arrow_with_text + mark_arrow_with_text
# No channel encoding options are specified in this chart
# so the code is the same as for the method-based syntax.