Getting the same subplot size using matplotlib imshow and scatter

It's not perfectly clear what your desired outcome is.

1. You may use automatic aspect on the image

   ax.imshow(z, aspect="auto")
   

   

2. Or you may set the aspect of the line plot depending on its axis limits such that it gets the same size as the image (in case the image has equal x and y sizes)

   asp = np.diff(ax2.get_xlim())[0] / np.diff(ax2.get_ylim())[0]
   ax2.set_aspect(asp)
   

   Complete code:

   import numpy as np
   import matplotlib.pyplot as plt
   
   x = np.linspace(0,10,20)
   y = np.sin(x)
   z = np.random.rand(100,100)
   
   fig, (ax, ax2) = plt.subplots(ncols=2)
   
   ax.imshow(z)
   ax2.plot(x,y, marker=".")
   
   asp = np.diff(ax2.get_xlim())[0] / np.diff(ax2.get_ylim())[0]
   ax2.set_aspect(asp)
   
   plt.show()
   

   If the image does not have equal limits (is not square), one still needs to divide by the aspect of the image:

   asp = np.diff(ax2.get_xlim())[0] / np.diff(ax2.get_ylim())[0]
   asp /= np.abs(np.diff(ax1.get_xlim())[0] / np.diff(ax1.get_ylim())[0])
   ax2.set_aspect(asp)
   

3. More sophisticated solutions:

   • This answer for using the subplot parameters to achieve a certain aspect.

   • If you want to use mpl_toolkits and make your hands dirty, this answer would be a good read.

I had the same problem and asked a very similar question in SO. The solution proposed by @ImportanceOfBeingErnest worked like a charm for me, but for completeness, I'd like to mention a pretty simple workaround I was suggested to apply (credit to @Yilun Zhang) before my question was marked as an exact duplicate of this one:

The problem is that the plot region height is too large and this is leaving empty place in the image.

If you change your code to:

fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(14, 6))

then you get the desired outcome:

Here's some code I use:

fig, axis_array = plt.subplots(1, 2, figsize=(chosen_value, 1.05 * chosen_value / 2),
                               subplot_kw={'aspect': 1})

I'm explicitly selecting that there will be 2 sub plots in my figure, and that the figure will be chosen_value tall and each subplot will be about half that size wide, and that the subplots will have an aspect ratio of 1 (i.e., they will both be square). The figure size is a specific ratio which forces the spacing.

For those sharing the y-axis across both plots, setting constrained_layout to True may help.