Matplotlib Tutorial - Place Text in the Plot

1. Matplotlib Axes Text
2. Matplotlib Axes Text Basic Example
3. Matplotlib Axes Text Rotation
4. Matplotlib Axes Text Rotation Angle Explanation

We will learn about how to place text in the plot in this tutorial. You would either add text and give that text a coordinate location or you can also add text to a specific plot and maybe draw an arrow that points directly to that plot.

Matplotlib Axes Text

matplotlib.axes.Axes.text(x, y, s, fontdict=None, withdash=False, **kwargs)

Add the text s to the axes at location (x, y) in data coordinates.

Parameters

Matplotlib Axes Text Basic Example

# -*- coding: utf-8 -*-
import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(0, 4 * np.pi, 1000)
y = 10 * np.sin(x)

fig, ax = plt.subplots(1, figsize=(6, 4.5))
ax.plot(x, y, "r")
ax.text(2.0, 9.5, "Peak Value", fontsize=14)

ax.grid(True)

plt.show()

Matplotlib Axes Text Rotation

The axes text has an keyword argument - rotation that specifies the text rotation angle in the plot. The rotation angle is between 0 and 360 (degree).

# -*- coding: utf-8 -*-
import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(0, 4 * np.pi, 1000)
y = 10 * np.sin(x)

fig, ax = plt.subplots(1, figsize=(6, 4.5))
ax.plot(x, y, "r")
ax.text(1.3, 9.0, "Peak Value", fontsize=16, rotation=270)

ax.grid(True)

plt.show()

Matplotlib Axes Text Rotation Angle Explanation

The rotation angle is in the direction of counter clockwise. We make a demo script to illustrate the rotation angle definition.

import matplotlib.pyplot as plt
import numpy as np


def addtext(ax, props):
    for x in range(8):
        angle = 45 * x
        ax.text(0.5 + x, 0.5, "{} degree".format(angle), props, rotation=angle)
        ax.scatter(x + 0.5, 0.5, color="r")

    ax.set_yticks([0, 0.5, 1])
    ax.set_xlim(0, 8)
    ax.grid(True)


# the text bounding box
bbox = {"fc": "0.8", "pad": 0}

fig, axs = plt.subplots(1, 1, figsize=(8, 3))

addtext(axs, {"ha": "center", "va": "center", "bbox": bbox})
axs.set_xticks(np.arange(0, 8.1, 0.5), [])
axs.set_ylabel("center / center")

plt.show()

The text is aligned by its bounding box that is the rectangular box surrounding the text rectangle. The text will be firstly rotated and then aligned. Basically, the text is centered at (x, y) location, rotated around this point, and then aligned according to the bounding box of the rotated text.

So if you specify left, bottom alignment, the bottom left of the bounding box of the rotated text will be at the (x, y) coordinate of the text.