Hide contour linestroke on pyplot.contourf to get only fills

Question

I have a pet project to create images of maps, where I draw the roads and other stuff over a contour plot of the terrain elevation. It is intended to plan mountain bike rout

Answer 1

I finally found a proper solution to this long-standing problem (currently in Matplotlib 3), which does not require multiple calls to contour or rasterizing the figure.

Note that the problem illustrated in the question appears only in saved publication-quality figures formats like PDF, not in lower-quality raster files like PNG.

My solution was inspired by this answer, related to a similar problem with the colorbar. A similar solution turns out to solve the contour plot as well, as follows:

import numpy as np
import matplotlib.pyplot as plt

np.random.seed(123)
x, y = np.random.uniform(size=(100, 2)).T
z = np.exp(-x**2 - y**2)
levels = np.linspace(0, 1, 100)

cnt = plt.tricontourf(x, y, z, levels=levels, cmap="ocean")

# This is the fix for the white lines between contour levels
for c in cnt.collections:
    c.set_edgecolor("face")

plt.savefig("test.pdf")    

Here below is an example of contours before the fix

And here below is the same figure after the above fix