creating a matplotlib scatter legend size related

Question

I am looking for a way to include a (matplotlib) legend that describe the size of points in a scatter plot, as this could be related to another variable, like in this basic

Answer 1

This'll also work, and I think it's a bit simpler:

msizes = np.array([3, 4, 5, 6, 7, 8])

l1, = plt.plot([],[], 'or', markersize=msizes[0])
l2, = plt.plot([],[], 'or', markersize=msizes[1])
l3, = plt.plot([],[], 'or', markersize=msizes[2])
l4, = plt.plot([],[], 'or', markersize=msizes[3])

labels = ['M3', 'M4', 'M5', 'M6']

leg = plt.legend([l1, l2, l3, l4], labels, ncol=1, frameon=True, fontsize=12,
handlelength=2, loc = 8, borderpad = 1.8,
handletextpad=1, title='My Title', scatterpoints = 1)

Taken from: Point size legends in matplotlib and basemap plots