Clip an image using several patches in matplotlib

Question

I have a plot in pylab which I want to clip to the borders of a map of the UK.

I've also made a series of patches which contain the outlines of each country: one for England, one for Wales etc.

Clipping the plot one patch works brilliantly:

fig = plt.figure()
ax = fig.add_subplot(111)
im = ax.scatter(x,y,c = z)
ax.add_patch(patch)
im.set_clip_path(patch)

But if I try and do it for more than one, it leaves me with nothing - understandably, since no part of the plot is within each country simultaneously.

Does anyone know how I can clip using an 'OR' type statement? (ie. don't clip if within this patch or this one etc).

Answer 1

I think you can do this by making multiple scatter plots, clipping each one with a unique patch (eg one has England, one has Ireland, etc). Though this might not be what you asked for, ie "Does anyone know how I can clip using an 'OR' type statement?", it should have the same effect:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.patches as patches

np.random.seed(101)
x = np.random.random(100)
y = np.random.random(100)

fig = plt.figure()
ax = fig.add_subplot(111)
imForEngland = ax.scatter(x,y)
fig.savefig('beforeclip.png')
imForWales = ax.scatter(x,y)
england = patches.Circle((.75,.75),radius=.25,fc='none')
wales = patches.Circle((.25,.25),radius=.25,fc='none')
ax.add_patch(england)
ax.add_patch(wales)
imForEngland.set_clip_path(england)
imForWales.set_clip_path(wales)

fig.savefig('afterclip.png')

Before the patches: After the patches: