Bug summary

Markers of different types ("o", "s", "*" ...) do not visually appear to be of the same size when their marker size (e.g. ms=8) is equal (matplotlib 3.1.1).

Details

Matplotlib has a great selection of markers, but the relative sizes of these markers are not perceptually uniform, see
https://matplotlib.org/3.1.1/api/markers_api.html
or this example script:

from matplotlib import pyplot as pltplt.style.use("default")import numpy as npx = np.arange(4)y = np.ones(4)for imarker, marker in enumerate("os*pv^<>PDdX"):    plt.plot(x, y + 0.1 * imarker, marker=marker)plt.show()

The square "s" and the diamond "D" appear larger than the other markers. The star "*" is the smallest, followed by the pentagon "p" and the plus "P".

Expected outcome

Markers should appear uniform in size. I think for the star this is very obviously not the case. The area of the star is much smaller than for the circle, and largest for the square and the diamond.

Nevertheless, I don't think an objective geometric criterion like area can be used to make them perceptually uniform in size. I think this needs to be hand-tuned by a human to take into account how humans perceive the relative size of objects.