Basic Pyramid Chart — Altair

A pyramid chart displays two opposing horizontal bar charts that share a central axis, creating a pyramid or butterfly shape. This visualization is ideal for comparing two related metrics across the same categories, revealing asymmetries and patterns in bidirectional data. Most commonly used for population pyramids showing age-gender distributions.

Basic Pyramid Chart rendered with Altair

Python source (Altair)

""" anyplot.ai
pyramid-basic: Basic Pyramid Chart
Library: altair 6.1.0 | Python 3.13.13
Quality: 90/100 | Updated: 2026-04-29
"""

import importlib
import os
import sys


# Drop script directory from sys.path so the `altair` package resolves, not this file
sys.path[:] = [p for p in sys.path if os.path.abspath(p or ".") != os.path.dirname(os.path.abspath(__file__))]
alt = importlib.import_module("altair")
pd = importlib.import_module("pandas")

# Theme tokens
THEME = os.getenv("ANYPLOT_THEME", "light")
PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
ELEVATED_BG = "#FFFDF6" if THEME == "light" else "#242420"
INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"

IMPRINT = ["#009E73", "#C475FD", "#4467A3", "#BD8233", "#AE3030", "#2ABCCD", "#954477"]

# Data — population pyramid with pronounced gender gap in older age groups
age_groups = ["0-9", "10-19", "20-29", "30-39", "40-49", "50-59", "60-69", "70-79", "80+"]
male = [4.8, 5.2, 6.1, 7.3, 8.5, 7.8, 5.9, 3.2, 1.2]
female = [4.5, 5.0, 6.3, 7.5, 8.7, 8.2, 6.8, 4.8, 2.5]  # more females in older groups

df = pd.DataFrame(
    {
        "Age Group": age_groups * 2,
        "Population": [-v for v in male] + female,
        "Gender": ["Male"] * len(age_groups) + ["Female"] * len(age_groups),
        "Absolute": male + female,
    }
)

age_order = list(reversed(age_groups))

# Interactive highlight — click legend to isolate a gender
selection = alt.selection_point(fields=["Gender"], bind="legend")

# Plot
chart = (
    alt.Chart(df)
    .mark_bar(cornerRadiusEnd=3)
    .encode(
        y=alt.Y("Age Group:N", sort=age_order, axis=alt.Axis(title="Age Group", titleFontSize=22, labelFontSize=18)),
        x=alt.X(
            "Population:Q",
            axis=alt.Axis(
                title="Population (millions)",
                titleFontSize=22,
                labelFontSize=18,
                values=[-8, -6, -4, -2, 0, 2, 4, 6, 8],
                labelExpr="abs(datum.value)",
            ),
            scale=alt.Scale(domain=[-10, 10]),
        ),
        color=alt.Color(
            "Gender:N",
            scale=alt.Scale(domain=["Male", "Female"], range=[IMPRINT[0], IMPRINT[1]]),
            legend=alt.Legend(title="Gender", titleFontSize=20, labelFontSize=18, orient="bottom"),
        ),
        opacity=alt.condition(selection, alt.value(0.9), alt.value(0.25)),
        tooltip=[
            alt.Tooltip("Gender:N"),
            alt.Tooltip("Age Group:N"),
            alt.Tooltip("Absolute:Q", title="Population (M)", format=".1f"),
        ],
    )
    .add_params(selection)
    .properties(
        width=1600,
        height=900,
        background=PAGE_BG,
        title=alt.Title(text="pyramid-basic · altair · anyplot.ai", fontSize=28, anchor="middle"),
    )
    .configure_view(fill=PAGE_BG, stroke=None)
    .configure_axis(
        domainColor=INK_SOFT, tickColor=INK_SOFT, gridColor=INK, gridOpacity=0.10, labelColor=INK_SOFT, titleColor=INK
    )
    .configure_title(color=INK)
    .configure_legend(
        fillColor=ELEVATED_BG,
        strokeColor=INK_SOFT,
        labelColor=INK_SOFT,
        titleColor=INK,
        titleFontSize=20,
        labelFontSize=18,
    )
)

# Save
chart.save(f"plot-{THEME}.png", scale_factor=3.0)
chart.save(f"plot-{THEME}.html")

Part of Basic Pyramid Chart on anyplot.ai.

Other implementations