Set Matplotlib colorbar size to match graph

Question

I cannot get the colorbar on imshow graphs like this one to be the same height as the graph  short of using Photoshop after the fact  How do I get the heights to match

User · Accepted Answer

You can do this easily with a matplotlib AxisDivider.

The example from the linked page also works without using subplots:

import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1 import make_axes_locatable
import numpy as np

plt.figure()
ax = plt.gca()
im = ax.imshow(np.arange(100).reshape((10,10)))

# create an axes on the right side of ax. The width of cax will be 5%
# of ax and the padding between cax and ax will be fixed at 0.05 inch.
divider = make_axes_locatable(ax)
cax = divider.append_axes("right", size="5%", pad=0.05)

plt.colorbar(im, cax=cax)

enter image description here

User · Answer

This combination  and values near to these  seems to  magically  work for me to keep the colorbar scaled to the plot  no matter what size the display   plt colorbar im fraction 0 046  pad 0 04    It also does not require sharing the axis which can get the plot out of square

User · Answer

When you create the colorbar try using the fraction and or shrink parameters   From the documents      fraction  0 15  fraction of original axes to use for colorbar       shrink    1 0  fraction by which to shrink the colorbar

User · Answer

I appreciate all the answers above  However  like some answers and comments pointed out  the axes grid1 module cannot address GeoAxes  whereas adjusting fraction  pad  shrink  and other similar parameters cannot necessarily give the very precise order  which really bothers me  I believe that giving the colorbar its own axes might be a better solution to address all the issues that have been mentioned   Code  import matplotlib pyplot as plt import numpy as np  fig plt figure   ax   plt axes   im   ax imshow np arange 100  reshape  10 10       Create an axes for colorbar  The position of the axes is calculated based on the position of ax    You can change 0 01 to adjust the distance between the main image and the colorbar    You can change 0 02 to adjust the width of the colorbar    This practice is universal for both subplots and GeoAxes   cax   fig add axes  ax get position   x1 0 01 ax get position   y0 0 02 ax get position   height   plt colorbar im  cax cax    Similar to fig colorbar im  cax   cax    Result    Later on  I find matplotlib pyplot colorbar official documentation also gives ax option  which are existing axes that will provide room for the colorbar  Therefore  it is useful for multiple subplots  see following   Code  fig  ax   plt subplots 2 1 figsize  12 8     Caution  figsize will also influence positions  im1   ax 0  imshow np arange 100  reshape  10 10    vmin   -100  vmax  100  im2   ax 1  imshow np arange -100 0  reshape  10 10    vmin   -100  vmax  100  fig colorbar im1  ax ax    Result    Again  you can also achieve similar effects by specifying cax  a more accurate way from my perspective   Code  fig  ax   plt subplots 2 1 figsize  12 8   im1   ax 0  imshow np arange 100  reshape  10 10    vmin   -100  vmax  100  im2   ax 1  imshow np arange -100 0  reshape  10 10    vmin   -100  vmax  100  cax   fig add axes  ax 1  get position   x1-0 25 ax 1  get position   y0 0 02 ax 0  get position   y1-ax 1  get position   y0   fig colorbar im1  cax cax    Result

User · Answer

bogatron already gave the answer suggested by the matplotlib docs  which produces the right height  but it introduces a different problem  Now the width of the colorbar  as well as the space between colorbar and plot  changes with the width of the plot  In other words  the aspect ratio of the colorbar is not fixed anymore   To get both the right height and a given aspect ratio  you have to dig a bit deeper into the mysterious axes grid1 module   import matplotlib pyplot as plt from mpl toolkits axes grid1 import make axes locatable  axes size import numpy as np  aspect   20 pad fraction   0 5  ax   plt gca   im   ax imshow np arange 200  reshape  20  10    divider   make axes locatable ax  width   axes size AxesY ax  aspect 1  aspect  pad   axes size Fraction pad fraction  width  cax   divider append axes  right   size width  pad pad  plt colorbar im  cax cax    Note that this specifies the width of the colorbar w r t  the height of the plot  in contrast to the width of the figure  as it was before    The spacing between colorbar and plot can now be specified as a fraction of the width of the colorbar  which is IMHO a much more meaningful number than a fraction of the figure width     UPDATE   I created an IPython notebook on the topic  where I packed the above code into an easily re-usable function   import matplotlib pyplot as plt from mpl toolkits import axes grid1  def add colorbar im  aspect 20  pad fraction 0 5    kwargs          Add a vertical color bar to an image plot         divider   axes grid1 make axes locatable im axes      width   axes grid1 axes size AxesY im axes  aspect 1  aspect      pad   axes grid1 axes size Fraction pad fraction  width      current ax   plt gca       cax   divider append axes  right   size width  pad pad      plt sca current ax      return im axes figure colorbar im  cax cax    kwargs    It can be used like this   im   plt imshow np arange 200  reshape  20  10    add colorbar im

User · Answer

All the above solutions are good  but I like  Steve s and  bejota s the best as they do not involve fancy calls and are universal    By universal I mean that works with any type of axes including GeoAxes  For example  it you have projected axes for mapping    projection   cartopy crs UTM zone  17N   ax   plt axes projection projection  im   ax imshow np arange 200  reshape  20  10      a call to   cax   divider append axes  right   size width  pad pad    will fail with  KeyException  map projection  Therefore  the only universal way of dealing colorbar size with all types of axes is   ax colorbar im  fraction 0 046  pad 0 04    Work with fraction from 0 035 to 0 046 to get your best size  However  the values for the fraction and paddig will need to be adjusted to get the best fit for your plot and  will differ depending if the orientation of the colorbar is in vertical position or horizontal

[python] Set Matplotlib colorbar size to match graph

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