How to plot scatter masked points and add a line demarking masked regions in Matplotlib?

To plot scattered masked points and add a line to demark the masked regions, we can take the following steps.

Steps

Set the figure size and adjust the padding between and around the subplots.
Create N, r0, x, y, area, c, r, area1and area2 data points using numpy.
Plot x and y data points using scatter() method.
To demark the maked regions, plot the curve using plot() method.
To display the figure, use show() method.

Example

import matplotlib.pyplot as plt
import numpy as np

plt.rcParams["figure.figsize"] = [7.50, 3.50]
plt.rcParams["figure.autolayout"] = True

N = 100
r0 = 0.6
x = 0.9 * np.random.rand(N)
y = 0.9 * np.random.rand(N)
area = (20 * np.random.rand(N))**2
c = np.sqrt(area)

r = np.sqrt(x ** 2 + y ** 2)
area1 = np.ma.masked_where(r < r0, area)
area2 = np.ma.masked_where(r >= r0, area)
plt.scatter(x, y, s=area1, marker='^', c=c)
plt.scatter(x, y, s=area2, marker='o', c=c)
theta = np.arange(0, np.pi / 2, 0.01)
plt.plot(r0 * np.cos(theta), r0 * np.sin(theta))

plt.show()