Placing Legends Outside Matplotlib Plots
Matplotlib is a powerful library for creating visualizations in Python. Legends play a crucial role in providing context to these visualizations, explaining what each line or marker represents. However, sometimes legends can become too large or crowded, hindering readability. In such scenarios, placing the legend outside the plot can improve clarity and aesthetics.
Matplotlib offers flexibility in legend placement through the bbox_to_anchor and loc parameters. This article explores three examples of placing the legend outside the plot, demonstrating different settings for each.
Example 1: Legend in Top Right Corner
Placing the legend in the top right corner is a common practice, as it preserves the plot layout and offers a compact display. To achieve this, we’ll use the bbox_to_anchor parameter to adjust the legend’s location and size.
Let’s start with a simple plot with an embedded legend:
import matplotlib.pyplot as plt
import numpy as np
# Data for plotting
x = np.linspace(0, 2 * np.pi, 100)
y = np.sin(x)
# Plot
plt.plot(x, y, label='sin(x)')
plt.legend(loc='upper left') # Legend inside plot
plt.show()
To move the legend outside the plot to the top right corner, we adjust the bbox_to_anchor and loc parameters:
import matplotlib.pyplot as plt
import numpy as np
# Data for plotting
x = np.linspace(0, 2 * np.pi, 100)
y = np.sin(x)
# Plot
plt.plot(x, y, label='sin(x)')
plt.legend(bbox_to_anchor=(1.05, 1), loc='upper left') # Legend outside plot
plt.show()
In this modified code, bbox_to_anchor=(1.05, 1) positions the legend 5% to the right and 100% up from the upper left corner of the plot. Setting loc='upper left' ensures the legend moves outside the plot in the desired direction.
Example 2: Legend in Bottom Right Corner
Another common placement for legends outside the plot is the bottom right corner. Similar to the top right corner, this position preserves the plot layout while keeping the legend concise.
To achieve this, we modify the code from Example 1:
import matplotlib.pyplot as plt
import numpy as np
# Data for plotting
x = np.linspace(0, 2 * np.pi, 100)
y = np.cos(x)
# Plot
plt.plot(x, y, label='cos(x)')
plt.legend(bbox_to_anchor=(1.05, 0), loc='lower left') # Legend outside plot
plt.show()
Here, bbox_to_anchor=(1.05, 0) shifts the legend 5% to the right and 0% down from the lower left corner. We use loc='lower left' to move it to the bottom right corner.
Example 3: Legend Above Plot
When dealing with plots containing numerous lines or data points, the legend can become extensive. In such cases, placing the legend above the plot can be beneficial. This technique creates a dedicated row for the legend, expanding the original plot to accommodate it.
To accomplish this, we introduce the mode, expand, and ncol parameters along with bbox_to_anchor and loc:
import matplotlib.pyplot as plt
import numpy as np
# Data for plotting
x = np.linspace(0, 2 * np.pi, 100)
y_sin = np.sin(x)
y_cos = np.cos(x)
# Plot
plt.plot(x, y_sin, label='sin(x)')
plt.plot(x, y_cos, label='cos(x)')
plt.legend(bbox_to_anchor=(0., 1.02, 1., .102), loc='lower left',
ncol=2, mode="expand", borderaxespad=0.)
plt.show()
In this code, bbox_to_anchor=(0., 1.02, 1., .102) places the legend in a separate row above the plot. loc='lower left' aligns this row with the plot’s lower left corner. mode="expand" adds a border at the top of the plot to make space for the legend, while ncol=2 creates two columns of legend entries for better display. borderaxespad reduces padding between the legend and the plot’s x-axis.
Additional Resources
For further exploration of legend customization in Matplotlib, the official documentation provides comprehensive details. Numerous online tutorials and examples offer creative approaches to legend placement, enhancing visualization aesthetics and information clarity. Explore these resources to discover additional ways to improve your visualizations using bbox_to_anchor and other techniques.
In conclusion, placing legends outside plots in Matplotlib is a valuable technique for optimizing visualizations with multiple data points or lines. By adjusting legend location, size, and appearance using bbox_to_anchor, loc, ncol, and mode parameters, you can create clear and concise data representations. The examples presented in this article demonstrate the placement of legends in the top right and bottom right corners, as well as above the plot. With the help of the official documentation and online tutorials, you can further explore and enhance your visualizations using custom legend placements.