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.