How to Share a Single Colorbar Across Multiple Matplotlib Subplots?

Sharing a Colorbar for Multiple Subplots in Matplotlib

When creating multiple subplots in Matplotlib, it can be desirable to display a common colorbar for all the plots, ensuring a consistent color scheme and referencing. This can be particularly useful when comparing the values and patterns across different subplots.

The Dilemma

One common issue when sharing a colorbar is the autocorrelation of individual colorbars, each resizing to accommodate both the plot and the colorbar within the subplot's boundary box. This can result in unevenly sized subplots that appear inconsistent.

Solution: Separating the Colorbar

The solution to this issue is to create a separate axis dedicated to the colorbar. This axis is then used to display the colorbar independently of the plots, giving more control over its size and position.

To implement this approach, follow these steps:

1. Use the subplots_adjust function to make room for the colorbar in the overall figure. This is done by specifying the right-hand side of the figure as a fraction of the figure's width, usually slightly below 1.0 to leave some margin.
2. Create a separate subplot axis for the colorbar using add_axes. This subplot should be positioned to the right of the main axes.
3. Use the colorbar function to create the colorbar in the separate axis, specifying the relevant axis in the cax parameter.
4. Hide the axis line and tick marks on the colorbar subplot to give the appearance of a stand-alone colorbar.

Here is an example code that demonstrates the approach:

import numpy as np
import matplotlib.pyplot as plt

fig, axes = plt.subplots(nrows=2, ncols=2)
for ax in axes.flat:
    im = ax.imshow(np.random.random((10,10)), vmin=0, vmax=1)

fig.subplots_adjust(right=0.8)
cbar_ax = fig.add_axes([0.85, 0.15, 0.05, 0.7])
fig.colorbar(im, cax=cbar_ax)

plt.show()

This code creates four subplots and places a single colorbar to the right of the subplots, as shown in the accompanying image. The colorbar shares the color scheme with the subplots, and its size and position are independent of the subplots.

By following these steps, it is possible to effectively share a single colorbar across multiple subplots, ensuring consistency and improving the presentation of the data.

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