How to Create Polar Plot in Matplotlib: Simple Guide

To create a polar plot in matplotlib, use subplot(projection='polar') to set polar coordinates, then plot data with plot(). This draws data points based on angles and radii on a circular graph.

Syntax

Use plt.subplot(projection='polar') to create a polar axes. Then use plot(theta, r) where theta is the angle in radians and r is the radius.

• plt.subplot(projection='polar'): sets up a polar coordinate system.
• theta: array of angles in radians.
• r: array of radius values.
• plot(): draws the line or points on the polar plot.

python

import matplotlib.pyplot as plt
import numpy as np

# Example data
theta = np.linspace(0, 2 * np.pi, 100)
r = np.abs(np.sin(theta))

ax = plt.subplot(projection='polar')
ax.plot(theta, r)
plt.show()

Example

This example shows how to plot a simple polar plot with angles from 0 to 2π and radius as sine of the angle.

python

import numpy as np
import matplotlib.pyplot as plt

# Create array of angles from 0 to 2*pi
theta = np.linspace(0, 2 * np.pi, 100)
# Radius is sine of angle
r = np.abs(np.sin(theta * 3))

# Create polar subplot
ax = plt.subplot(projection='polar')
# Plot data
ax.plot(theta, r)

plt.title('Simple Polar Plot')
plt.show()

Output

A circular plot with three wave-like peaks around the circle, labeled 'Simple Polar Plot'.

Common Pitfalls

Common mistakes include:

• Using degrees instead of radians for angles. Matplotlib expects radians.
• Not setting projection='polar' in subplot(), which creates a normal plot instead of polar.
• Mixing up radius and angle arrays in plot().

Always convert degrees to radians with np.radians() if needed.

python

import numpy as np
import matplotlib.pyplot as plt

# Wrong: using degrees directly
theta_deg = np.linspace(0, 360, 100)
r = np.abs(np.sin(np.radians(theta_deg * 3)))

# Wrong: no polar projection
plt.subplot(111)
plt.plot(theta_deg, r)  # This will not create a polar plot
plt.title('Wrong Plot')
plt.show()

# Correct way
theta_rad = np.radians(theta_deg)
plt.subplot(projection='polar')
plt.plot(theta_rad, r)
plt.title('Correct Polar Plot')
plt.show()

Output

First plot: a normal Cartesian plot with angle degrees on x-axis and radius on y-axis.
Second plot: a circular polar plot with correct angle-radius mapping.

Quick Reference

Remember these key points for polar plots in Matplotlib:

• Use projection='polar' in subplot().
• Angles must be in radians.
• Radius values define distance from center.
• Use plot(theta, r) to draw lines.
• Use scatter(theta, r) for points.

Key Takeaways

Use plt.subplot(projection='polar') to create polar coordinate axes.

Angles must be in radians, not degrees, for polar plots.

Plot data with ax.plot(theta, r) where theta is angle and r is radius.

Common errors include forgetting polar projection or using degrees directly.

Polar plots show data in circular form based on angle and radius.