A ternary plot displays three-component compositional data on an equilateral triangle where each vertex represents 100% of one component. Points inside the triangle show compositions that sum to a constant total (usually 100%), with position indicating relative proportions. This visualization is essential for data where three variables are interdependent and constrained to sum to a fixed value.
""" anyplot.ai
ternary-basic: Basic Ternary Plot
Library: matplotlib 3.10.9 | Python 3.13.13
Quality: 95/100 | Updated: 2026-05-06
"""
import os
import sys
if sys.path and (sys.path[0] == "" or sys.path[0].endswith("/python")):
sys.path.pop(0)
import matplotlib.pyplot as plt
import numpy as np
# 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"
BRAND = "#009E73"
# Data - Soil composition samples (sand, silt, clay summing to 100%)
np.random.seed(42)
n_points = 60
# Generate compositions with better edge/corner coverage using Dirichlet
# Lower alpha values concentrate points at edges; higher values favor center
# Use alpha=1 for more uniform distribution across the simplex
raw = np.random.dirichlet([1, 1, 1], n_points) * 100
sand = raw[:, 0]
silt = raw[:, 1]
clay = raw[:, 2]
# Convert ternary coordinates to Cartesian (equilateral triangle)
# Triangle: Sand at top (0.5, sqrt(3)/2), Silt at bottom-left (0, 0), Clay at bottom-right (1, 0)
sqrt3_2 = np.sqrt(3) / 2
total = sand + silt + clay
x_points = 0.5 * (2 * clay + sand) / total
y_points = sqrt3_2 * sand / total
# Create figure (square format for triangle)
fig, ax = plt.subplots(figsize=(12, 12), facecolor=PAGE_BG)
ax.set_facecolor(PAGE_BG)
# Draw triangle outline
triangle_x = [0.5, 0, 1, 0.5]
triangle_y = [sqrt3_2, 0, 0, sqrt3_2]
ax.plot(triangle_x, triangle_y, color=INK_SOFT, linewidth=2.5)
# Draw grid lines at 20% intervals
grid_levels = [0.2, 0.4, 0.6, 0.8]
for level in grid_levels:
# Lines parallel to bottom edge (constant sand)
a_val = level
x1 = 0.5 * (2 * (1 - a_val) + a_val)
y1 = sqrt3_2 * a_val
x2 = 0.5 * (2 * 0 + a_val)
y2 = sqrt3_2 * a_val
ax.plot([x1, x2], [y1, y2], color=INK_SOFT, alpha=0.15, linewidth=1.2, linestyle="--")
# Lines parallel to right edge (constant silt)
b_val = level
x1 = 0.5 * (2 * (1 - b_val) + 0)
y1 = sqrt3_2 * 0
x2 = 0.5 * (2 * 0 + (1 - b_val))
y2 = sqrt3_2 * (1 - b_val)
ax.plot([x1, x2], [y1, y2], color=INK_SOFT, alpha=0.15, linewidth=1.2, linestyle="--")
# Lines parallel to left edge (constant clay)
c_val = level
x1 = 0.5 * (2 * c_val + 0)
y1 = sqrt3_2 * 0
x2 = 0.5 * (2 * c_val + (1 - c_val))
y2 = sqrt3_2 * (1 - c_val)
ax.plot([x1, x2], [y1, y2], color=INK_SOFT, alpha=0.15, linewidth=1.2, linestyle="--")
# Add tick labels at 20% intervals along each edge
tick_fontsize = 14
for level in [0, 20, 40, 60, 80, 100]:
frac = level / 100
# Sand axis (A) - along left edge from bottom to top
x_tick = 0.5 * (2 * 0 + frac)
y_tick = sqrt3_2 * frac
ax.text(x_tick - 0.06, y_tick, f"{level}", fontsize=tick_fontsize, ha="right", va="center", color=INK_SOFT)
# Silt axis (B) - along bottom edge from right to left
x_tick = 0.5 * (2 * (1 - frac) + 0)
y_tick = 0
ax.text(x_tick, y_tick - 0.05, f"{level}", fontsize=tick_fontsize, ha="center", va="top", color=INK_SOFT)
# Clay axis (C) - along right edge from top to bottom
x_tick = 0.5 * (2 * frac + (1 - frac))
y_tick = sqrt3_2 * (1 - frac)
ax.text(x_tick + 0.06, y_tick, f"{level}", fontsize=tick_fontsize, ha="left", va="center", color=INK_SOFT)
# Plot data points
ax.scatter(x_points, y_points, s=220, color=BRAND, alpha=0.75, edgecolors=PAGE_BG, linewidth=1.2, zorder=5)
# Add vertex labels with component names
label_fontsize = 20
ax.text(
0.5, sqrt3_2 + 0.12, "Sand (%)", fontsize=label_fontsize, ha="center", va="bottom", fontweight="bold", color=INK
)
ax.text(-0.1, -0.1, "Silt (%)", fontsize=label_fontsize, ha="right", va="top", fontweight="bold", color=INK)
ax.text(1.1, -0.1, "Clay (%)", fontsize=label_fontsize, ha="left", va="top", fontweight="bold", color=INK)
# Title
ax.set_title("ternary-basic · matplotlib · anyplot.ai", fontsize=24, fontweight="medium", color=INK, pad=20)
# Clean up axes
ax.set_aspect("equal")
ax.axis("off")
# Adjust limits to prevent clipping
ax.set_xlim(-0.28, 1.28)
ax.set_ylim(-0.22, 1.15)
plt.tight_layout()
plt.savefig(f"plot-{THEME}.png", dpi=300, bbox_inches="tight", facecolor=PAGE_BG)
Part of Basic Ternary Plot on anyplot.ai.