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"""
.. _colorbar_placement:
.. redirect-from:: /gallery/subplots_axes_and_figures/colorbar_placement
=================
Placing colorbars
=================
Colorbars indicate the quantitative extent of image data. Placing in
a figure is non-trivial because room needs to be made for them.
Automatic placement of colorbars
================================
The simplest case is just attaching a colorbar to each Axes. Note in this
example that the colorbars steal some space from the parent Axes.
"""
import matplotlib.pyplot as plt
import numpy as np
# Fixing random state for reproducibility
np.random.seed(19680801)
fig, axs = plt.subplots(2, 2)
cmaps = ['RdBu_r', 'viridis']
for col in range(2):
for row in range(2):
ax = axs[row, col]
pcm = ax.pcolormesh(np.random.random((20, 20)) * (col + 1),
cmap=cmaps[col])
fig.colorbar(pcm, ax=ax)
# %%
# The first column has the same type of data in both rows, so it may be
# desirable to have just one colorbar. We do this by passing `.Figure.colorbar`
# a list of Axes with the *ax* kwarg.
fig, axs = plt.subplots(2, 2)
cmaps = ['RdBu_r', 'viridis']
for col in range(2):
for row in range(2):
ax = axs[row, col]
pcm = ax.pcolormesh(np.random.random((20, 20)) * (col + 1),
cmap=cmaps[col])
fig.colorbar(pcm, ax=axs[:, col], shrink=0.6)
# %%
# The stolen space can lead to Axes in the same subplot layout
# being different sizes, which is often undesired if the the
# x-axis on each plot is meant to be comparable as in the following:
fig, axs = plt.subplots(2, 1, figsize=(4, 5), sharex=True)
X = np.random.randn(20, 20)
axs[0].plot(np.sum(X, axis=0))
pcm = axs[1].pcolormesh(X)
fig.colorbar(pcm, ax=axs[1], shrink=0.6)
# %%
# This is usually undesired, and can be worked around in various ways, e.g.
# adding a colorbar to the other Axes and then removing it. However, the most
# straightforward is to use :ref:`constrained layout <constrainedlayout_guide>`:
fig, axs = plt.subplots(2, 1, figsize=(4, 5), sharex=True, layout='constrained')
axs[0].plot(np.sum(X, axis=0))
pcm = axs[1].pcolormesh(X)
fig.colorbar(pcm, ax=axs[1], shrink=0.6)
# %%
# Relatively complicated colorbar layouts are possible using this
# paradigm. Note that this example works far better with
# ``layout='constrained'``
fig, axs = plt.subplots(3, 3, layout='constrained')
for ax in axs.flat:
pcm = ax.pcolormesh(np.random.random((20, 20)))
fig.colorbar(pcm, ax=axs[0, :2], shrink=0.6, location='bottom')
fig.colorbar(pcm, ax=[axs[0, 2]], location='bottom')
fig.colorbar(pcm, ax=axs[1:, :], location='right', shrink=0.6)
fig.colorbar(pcm, ax=[axs[2, 1]], location='left')
# %%
# Adjusting the spacing between colorbars and parent Axes
# =======================================================
#
# The distance a colorbar is from the parent Axes can be adjusted with the
# *pad* keyword argument. This is in units of fraction of the parent Axes
# width, and the default for a vertical Axes is 0.05 (or 0.15 for a horizontal
# Axes).
fig, axs = plt.subplots(3, 1, layout='constrained', figsize=(5, 5))
for ax, pad in zip(axs, [0.025, 0.05, 0.1]):
pcm = ax.pcolormesh(np.random.randn(20, 20), cmap='viridis')
fig.colorbar(pcm, ax=ax, pad=pad, label=f'pad: {pad}')
fig.suptitle("layout='constrained'")
# %%
# Note that if you do not use constrained layout, the pad command makes the
# parent Axes shrink:
fig, axs = plt.subplots(3, 1, figsize=(5, 5))
for ax, pad in zip(axs, [0.025, 0.05, 0.1]):
pcm = ax.pcolormesh(np.random.randn(20, 20), cmap='viridis')
fig.colorbar(pcm, ax=ax, pad=pad, label=f'pad: {pad}')
fig.suptitle("No layout manager")
# %%
# Manual placement of colorbars
# =============================
#
# Sometimes the automatic placement provided by ``colorbar`` does not
# give the desired effect. We can manually create an Axes and tell
# ``colorbar`` to use that Axes by passing the Axes to the *cax* keyword
# argument.
#
# Using ``inset_axes``
# --------------------
#
# We can manually create any type of Axes for the colorbar to use, but an
# `.Axes.inset_axes` is useful because it is a child of the parent Axes and can
# be positioned relative to the parent. Here we add a colorbar centered near
# the bottom of the parent Axes.
fig, ax = plt.subplots(layout='constrained', figsize=(4, 4))
pcm = ax.pcolormesh(np.random.randn(20, 20), cmap='viridis')
ax.set_ylim([-4, 20])
cax = ax.inset_axes([0.3, 0.07, 0.4, 0.04])
fig.colorbar(pcm, cax=cax, orientation='horizontal')
# %%
# `.Axes.inset_axes` can also specify its position in data coordinates
# using the *transform* keyword argument if you want your Axes at a
# certain data position on the graph:
fig, ax = plt.subplots(layout='constrained', figsize=(4, 4))
pcm = ax.pcolormesh(np.random.randn(20, 20), cmap='viridis')
ax.set_ylim([-4, 20])
cax = ax.inset_axes([7.5, -1.7, 5, 1.2], transform=ax.transData)
fig.colorbar(pcm, cax=cax, orientation='horizontal')
# %%
# Colorbars attached to fixed-aspect-ratio Axes
# ---------------------------------------------
#
# Placing colorbars for Axes with a fixed aspect ratio pose a particular
# challenge as the parent Axes changes size depending on the data view.
fig, axs = plt.subplots(2, 2, layout='constrained')
cmaps = ['RdBu_r', 'viridis']
for col in range(2):
for row in range(2):
ax = axs[row, col]
pcm = ax.pcolormesh(np.random.random((20, 20)) * (col + 1),
cmap=cmaps[col])
if col == 0:
ax.set_aspect(2)
else:
ax.set_aspect(1/2)
if row == 1:
fig.colorbar(pcm, ax=ax, shrink=0.6)
# %%
# We solve this problem using `.Axes.inset_axes` to locate the Axes in "axes
# coordinates" (see :ref:`transforms_tutorial`). Note that if you zoom in on
# the parent Axes, and thus change the shape of it, the colorbar will also
# change position.
fig, axs = plt.subplots(2, 2, layout='constrained')
cmaps = ['RdBu_r', 'viridis']
for col in range(2):
for row in range(2):
ax = axs[row, col]
pcm = ax.pcolormesh(np.random.random((20, 20)) * (col + 1),
cmap=cmaps[col])
if col == 0:
ax.set_aspect(2)
else:
ax.set_aspect(1/2)
if row == 1:
cax = ax.inset_axes([1.04, 0.2, 0.05, 0.6])
fig.colorbar(pcm, cax=cax)
# %%
# .. seealso::
#
# :ref:`axes_grid` has methods for manually creating colorbar Axes as well:
#
# - :ref:`demo-colorbar-with-inset-locator`
# - :ref:`demo-colorbar-with-axes-divider`
|
