Matplotlib rasterized=True demonstration.

plot.py

import matplotlib.pyplot as plt
import numpy as np

n = 100000
x = np.random.normal(size=n)
y = np.random.normal(size=n)

pkw = {"marker": "o", "alpha": 0.1, "mew": 0, "ms": 2, "ls": ""}

fig, ax = plt.subplots(nrows=1)
ax.plot(x, y, **pkw)
ax.set_aspect("equal")
plt.savefig("scatter.pdf")

fig, ax = plt.subplots(nrows=1)
ax.plot(x, y, "o", **pkw, rasterized=True)
ax.set_aspect("equal")
plt.savefig("scatter-rasterized.pdf", dpi=600)