Setting axes limits

4.7. Setting axes limits#

When we create a plot interactively, we can zoom on a particular section using the figure’s Zoom and Pan buttons. It is also possible to zoom programmatically while we create the figure, using plt.axis.

4.7.1. Rectangular zoom#

Let’s create some random data:

import matplotlib.pyplot as plt

random_data = [
    0.60921838, 0.80049539, 0.11593785, 0.90703271, 0.75252107,
    0.72976933, 0.93364321, 0.14401492, 0.35255034, 0.68628490,
    0.76262073, 0.48124243, 0.73965093, 0.21237858, 0.63081351,
    0.75098067, 0.87658458, 0.68637267, 0.30947229, 0.19968510,
    0.59710015, 0.98464582, 0.05031455, 0.56996651, 0.74360835,
    0.30706612, 0.92693383, 0.63387122, 0.30740088, 0.46847444,
    0.99559865, 0.84777408, 0.21486266, 0.65472302, 0.51600203,
    0.3724475 , 0.0579805 , 0.62423827, 0.33997655, 0.14256265,
    0.5013935 , 0.98862076, 0.58028518, 0.15716675, 0.83572021,
    0.0119542 , 0.7257411 , 0.99901993, 0.69608303, 0.46573617
]

plt.plot(random_data, "o-");
_images/257106e60567d149495bfcbcff4b995acc9d96d53623331785c1290145a28dd1.png

To zoom on a specific portion of the plot, we call plt.axis, which takes for argument a list containing [xmin, xmax, ymin, ymax]. For example, to better see the portion between \(x \geq 20\) and \(x \leq 30\):

plt.plot(random_data, "o-")
plt.axis([20, 30, 0, 1]);
_images/feb857b3097c60d34fb7aa98b393b76321d1950b9aafcfa5cde0b420da4f0c93.png

4.7.2. Square zoom#

By defaults, plots are rectangular and will adapt their shape to optimize the scale on both x and y axes. However, in some circumstances, we need both x and y axes to have the same scale, e.g., to plot the (x, y) trajectory of a point in space. To set the same scale to both axes, we use plt.axis("square").

For example, plotting the (x, y) coordinates of a true circle looks like an ellipse by default:

x = [ 1.        ,  0.96592583,  0.8660254 ,  0.70710678,  0.5       ,
      0.25881905,  0.        , -0.25881905, -0.5       , -0.70710678,
     -0.8660254 , -0.96592583, -1.        , -0.96592583, -0.8660254 ,
     -0.70710678, -0.5       , -0.25881905, -0.        ,  0.25881905,
      0.5       ,  0.70710678,  0.8660254 ,  0.96592583,  1.        ]
     
y = [ 0.        ,  0.25881905,  0.5       ,  0.70710678,  0.8660254 ,
      0.96592583,  1.        ,  0.96592583,  0.8660254 ,  0.70710678,
      0.5       ,  0.25881905,  0.        , -0.25881905, -0.5       ,
     -0.70710678, -0.8660254 , -0.96592583, -1.        , -0.96592583,
     -0.8660254 , -0.70710678, -0.5       , -0.25881905, -0.        ]
     
plt.plot(x, y, "o-");
_images/6029711b6016eded5c46254c509e18bdbd9211e7f2a95a0a89ead83cdaffed25.png

This is solved by setting the axis to “square”:

plt.plot(x, y, "o-")
plt.axis("square");
_images/5cc94939a9b736d56f813947ea1e0405a97b72496a3e2390782207b20566f64f.png
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