Question

I’m fed up with manually creating graphs in excel and consequently, I’m trying to automate the process using Python to massage the .csv data into a workable form and matplotlib to plot the result.

Using matplotlib and generating them is no problem but I can’t work out is how to set the aspect ration / resolution of the output.

Specifically, I’m trying to generate scatter plots and stacked area graphs. Everything I’ve tried seems to result in one or more of the following:

• Cramped graph areas (small plot area covered with the legend, axes etc.).
• The wrong aspect ratio.
• Large spaces on the sides of the chart area (I want a very wide / not very tall image).

If anyone has some working examples showing how to achieve this result I’d be very grateful!

Answer 1

You can control the aspect ratio with ax.set_aspect:

import matplotlib.pyplot as plt
import numpy as np

fig = plt.figure()
ax=fig.add_subplot(1,1,1)
ax.set_aspect(0.3)
x,y=np.random.random((2,100))
plt.scatter(x,y)    

Another way to set the aspect ratio (already mentioned by jterrace) is to use the figsize parameter in plt.figure: e.g. fig = plt.figure(figsize=(3,1)). The two methods are slightly different however: A figure can contain many axes. figsize controls the aspect ratio for the entire figure, while set_aspect controls the aspect ratio for a particular axis.

Next, you can trim unused space from around the plot with bbox_inches='tight':

plt.savefig('/tmp/test.png', bbox_inches='tight')

If you want to get rid of the excess empty space due to matplotlib’s automated choice of x-range and y-range, you can manually set them with ax.set_xlim and ax.set_ylim:

ax.set_xlim(0, 1)
ax.set_ylim(0, 1)