Polar Plot with Legend

Introduction

In this lab, you will learn how to create a polar plot with a legend using Python Matplotlib. Polar plots are used to plot data in polar coordinates, which is useful when working with directional data. Legends are used to explain the meaning of the different lines or markers on a plot.

VM Tips

After the VM startup is done, click the top left corner to switch to the Notebook tab to access Jupyter Notebook for practice.

Sometimes, you may need to wait a few seconds for Jupyter Notebook to finish loading. The validation of operations cannot be automated because of limitations in Jupyter Notebook.

If you face issues during learning, feel free to ask Labby. Provide feedback after the session, and we will promptly resolve the problem for you.

Skills Graph

Import Libraries

The first step is to import the necessary libraries. In this example, we will be using numpy and matplotlib.

import matplotlib.pyplot as plt
import numpy as np

Create a Figure and Subplot

Next, we need to create a figure and subplot for our plot. We will be using the projection parameter of add_subplot to create a polar plot.

fig = plt.figure()
ax = fig.add_subplot(projection="polar", facecolor="lightgoldenrodyellow")

Create Data

We need to create some data to plot on our polar plot. In this example, we will create two lines.

r = np.linspace(0, 3, 301)
theta = 2 * np.pi * r

Plot Data

Now we can plot our data using the plot function. We will create two lines using the data we created in step 3.

ax.plot(theta, r, color="tab:orange", lw=3, label="a line")
ax.plot(0.5 * theta, r, color="tab:blue", ls="--", lw=3, label="another line")

Customize Plot

We can customize our plot by changing the grid color and adding a legend. In this example, we will move the legend slightly away from the center of the plot to avoid overlap.

ax.tick_params(grid_color="palegoldenrod")
angle = np.deg2rad(67.5)
ax.legend(loc="lower left",
          bbox_to_anchor=(.5 + np.cos(angle)/2, .5 + np.sin(angle)/2))

Display Plot

Finally, we can display our plot using the show function.

plt.show()

Summary

In this lab, you learned how to create a polar plot with a legend using Python Matplotlib. You also learned how to customize the plot by changing the grid color and moving the legend. Polar plots are useful when working with directional data and legends are useful for explaining the meaning of the different lines or markers on a plot.