A streamgraph (also known as a stacked area chart with a centered baseline) displaying the composition of multiple categories over time with smooth, flowing curves. Unlike traditional stacked area charts, streamgraphs use a symmetric baseline centered around the x-axis, creating an organic, river-like appearance that emphasizes the overall shape and relative proportions of each category while minimizing the visual distortion of individual layers.
""" anyplot.ai
streamgraph-basic: Basic Stream Graph
Library: pygal 3.1.0 | Python 3.13.13
Quality: 82/100 | Updated: 2026-05-06
"""
import os
import sys
# Remove script directory from sys.path so 'import pygal' finds the installed package
_script_dir = os.path.dirname(os.path.abspath(__file__))
sys.path = [p for p in sys.path if os.path.abspath(p) != _script_dir]
import numpy as np
import pygal
from pygal.style import Style
# Theme tokens
THEME = os.getenv("ANYPLOT_THEME", "light")
PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
INK_MUTED = "#6B6A63" if THEME == "light" else "#A8A79F"
IMPRINT = ("#009E73", "#C475FD", "#4467A3", "#BD8233", "#AE3030")
# Prepend background color for the invisible baseline series, then Okabe-Ito for genres
COLORS = (PAGE_BG,) + IMPRINT
# Data: monthly streaming hours by music genre over two years
np.random.seed(42)
months = 24
month_labels = [
"Jan 23",
"Feb 23",
"Mar 23",
"Apr 23",
"May 23",
"Jun 23",
"Jul 23",
"Aug 23",
"Sep 23",
"Oct 23",
"Nov 23",
"Dec 23",
"Jan 24",
"Feb 24",
"Mar 24",
"Apr 24",
"May 24",
"Jun 24",
"Jul 24",
"Aug 24",
"Sep 24",
"Oct 24",
"Nov 24",
"Dec 24",
]
genres = ["Pop", "Rock", "Hip-Hop", "Electronic", "Jazz"]
base_values = {"Pop": 45, "Rock": 35, "Hip-Hop": 40, "Electronic": 30, "Jazz": 15}
data = {}
for genre in genres:
base = base_values[genre]
trend = np.linspace(0, np.random.uniform(-10, 15), months)
seasonal = 8 * np.sin(np.linspace(0, 4 * np.pi, months) + np.random.uniform(0, 2 * np.pi))
noise = np.random.randn(months) * 3
values = base + trend + seasonal + noise
values = np.maximum(values, 5)
data[genre] = values.tolist()
# True streamgraph baseline: center the entire stack symmetrically around y=0.
# baseline[t] = -total[t]/2 so the stack spans from -total/2 to +total/2.
data_array = np.array([data[genre] for genre in genres])
total_at_each_time = data_array.sum(axis=0)
baseline = (-total_at_each_time / 2).tolist()
# Symmetric y-axis range with a small margin
half_total_max = total_at_each_time.max() / 2
y_range = half_total_max * 1.12
# Style
custom_style = Style(
background=PAGE_BG,
plot_background=PAGE_BG,
foreground=INK,
foreground_strong=INK,
foreground_subtle=INK_MUTED,
colors=COLORS,
title_font_size=28,
label_font_size=22,
major_label_font_size=18,
legend_font_size=16,
value_font_size=14,
stroke_width=3,
opacity=0.88,
opacity_hover=0.95,
)
# Chart
chart = pygal.StackedLine(
width=4800,
height=2700,
title="streamgraph-basic · pygal · anyplot.ai",
x_title="Month",
y_title="Streaming Hours",
style=custom_style,
fill=True,
show_dots=False,
show_y_guides=True,
show_x_guides=False,
legend_at_bottom=True,
legend_box_size=30,
margin=100,
spacing=40,
truncate_legend=-1,
truncate_label=-1,
interpolate="cubic",
show_minor_x_labels=False,
x_label_rotation=45,
range=(-y_range, y_range),
)
chart.x_labels = month_labels
chart.x_labels_major = ["Jan 23", "Jul 23", "Jan 24", "Jul 24"]
# Invisible baseline series shifts the stack so genres span -total/2 to +total/2.
# Color matches background (PAGE_BG) so it renders as transparent.
chart.add("", baseline)
# Genre series added with actual positive values — pygal stacks them on top of baseline
for genre in genres:
chart.add(genre, data[genre])
# Save
chart.render_to_png(f"plot-{THEME}.png")
with open(f"plot-{THEME}.html", "wb") as f:
f.write(chart.render())
Part of Basic Stream Graph on anyplot.ai.