Draw axis lines or the origin for Matplotlib contour plot.

To draw axis lines or the origin for matplotlib contour plot, we can use contourf(), axhline() for horizontal lines at y=0, and axvline() for vertical lines at x=0.

Steps to Create Contour Plot with Origin Lines

• Create data points for x, y, and z using numpy

• Set the figure properties using plt.rcParams

• Use contourf() method to create filled contour plot

• Plot x=0 and y=0 lines using axhline() and axvline()

• Display the figure using show() method

Example

Let's create a contour plot with origin axis lines ?

import numpy as np
import matplotlib.pyplot as plt

# Set figure properties
plt.rcParams["figure.figsize"] = [7.00, 3.50]
plt.rcParams["figure.autolayout"] = True

# Create coordinate data
x = np.linspace(-1.0, 1.0, 10)
x, y = np.meshgrid(x, x)
z = -np.hypot(x, y)

# Turn off axis
plt.axis('off')

# Create contour plot
plt.contourf(x, y, z, 10)

# Add origin lines
plt.axhline(0, color='red', linewidth=1)
plt.axvline(0, color='red', linewidth=1)

plt.show()

Understanding the Components

Key Functions

• np.meshgrid() − Creates coordinate matrices from coordinate vectors

• np.hypot() − Calculates the Euclidean distance (hypotenuse)

• contourf() − Creates filled contour plots

• axhline() − Adds horizontal line at specified y-value

• axvline() − Adds vertical line at specified x-value

Customizing Origin Lines

You can customize the appearance of the origin lines ?

import numpy as np
import matplotlib.pyplot as plt

plt.rcParams["figure.figsize"] = [8.00, 6.00]

x = np.linspace(-2.0, 2.0, 20)
x, y = np.meshgrid(x, x)
z = np.sin(x**2 + y**2)

# Create contour plot
plt.contourf(x, y, z, levels=15, cmap='viridis')

# Customize origin lines
plt.axhline(0, color='white', linewidth=2, linestyle='--', alpha=0.8)
plt.axvline(0, color='white', linewidth=2, linestyle='--', alpha=0.8)

plt.colorbar(label='Z values')
plt.title('Contour Plot with Custom Origin Lines')
plt.show()

Parameters for Origin Lines

Conclusion

Use axhline(0) and axvline(0) to add origin lines to contour plots. Customize the appearance with color, linewidth, and linestyle parameters for better visualization.