Annotation Box in Matplotlib

Annotation box is a feature in Matplotlib that allows you to add annotations to your plots with a box around them for emphasis. In this article, we will explore how to use annotation box in Matplotlib using various examples.

Basic Annotation Box

Let’s start with a basic example of adding an annotation box to a plot.

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [1, 4, 9, 16])

ax.annotate('This point', (3, 9), xytext=(4, 10),
             arrowprops=dict(facecolor='black', shrink=0.05))

plt.show()

Output:

In this example, we have a simple line plot with an annotation box added at the point (3, 9) with the text “This point”.

Customizing Annotation Box

You can customize the appearance of the annotation box by changing various properties such as text color, box color, arrow style, etc. Here’s an example:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [1, 4, 9, 16])

bbox_props = dict(boxstyle="round,pad=0.3", fc="cyan", ec="b", lw=2)
arrow_props = dict(arrowstyle="->")

ax.annotate('How2matplotlib.com', (2, 4), xytext=(3, 6),
             bbox=bbox_props, arrowprops=arrow_props, fontsize=12, color='red')

plt.show()

Output:

In this example, we have customized the appearance of the annotation box by changing the box style to “round”, box color to cyan, edge color to blue, arrow style to “->”, text color to red, and font size to 12.

Multiple Annotation Boxes

You can add multiple annotation boxes to a plot at different positions. Here’s an example with two annotation boxes:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [1, 4, 9, 16])

ax.annotate('How2matplotlib.com', (3, 9), xytext=(4, 12),
             arrowprops=dict(facecolor='black', shrink=0.05))

ax.annotate('Another point', (1, 1), xytext=(0.5, 2),
             arrowprops=dict(facecolor='green', shrink=0.05))

plt.show()

Output:

In this example, we have added two annotation boxes to the plot at points (3, 9) and (1, 1).

Annotation Box with ConnectionPatch

You can also use ConnectionPatch to connect the annotation box to a specific point on the plot. Here’s an example:

import matplotlib.pyplot as plt
from matplotlib.patches import ConnectionPatch

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [1, 4, 9, 16])

xy = (3, 9)
con = ConnectionPatch(xyA=xy, xyB=xy, coordsA="data", coordsB="data",
                      axesA=ax, axesB=ax, color="cyan", lw=2)

ax.add_artist(con)

plt.annotate('How2matplotlib.com', (3, 9), xytext=(4, 10),
             arrowprops=dict(facecolor='black', shrink=0.05))

plt.show()

Output:

In this example, we have used ConnectionPatch to connect the annotation box to the point (3, 9).

Adding Annotation Box to Specific Axes

You can add annotation boxes to specific axes in a plot with multiple subplots. Here’s an example:

import matplotlib.pyplot as plt

fig, (ax1, ax2) = plt.subplots(1, 2)
ax1.plot([1, 2, 3, 4], [1, 4, 9, 16])
ax2.plot([1, 2, 3, 4], [16, 9, 4, 1])

ax1.annotate('How2matplotlib.com', (3, 9), xytext=(4, 10),
              arrowprops=dict(facecolor='black', shrink=0.05))

ax2.annotate('Another point', (1, 16), xytext=(1.5, 14),
              arrowprops=dict(facecolor='green', shrink=0.05))

plt.show()

Output:

In this example, we have added annotation boxes to specific axes ax1 and ax2 in a plot with two subplots.

Annotation Box with Background Color

You can highlight the annotation box by adding a background color to it. Here’s an example:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [1, 4, 9, 16])

bbox_props = dict(boxstyle="round,pad=0.3", fc="yellow", ec="black", lw=2)
arrow_props = dict(arrowstyle="->")

ax.annotate('How2matplotlib.com', (2, 4), xytext=(3, 6),
             bbox=bbox_props, arrowprops=arrow_props)

plt.show()

Output:

In this example, we have added a yellow background color to the annotation box.

Annotation Box with Shadow

You can add a shadow effect to the annotation box to make it stand out more. Here’s an example:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [1, 4, 9, 16])

bbox_props = dict(boxstyle="round,pad=0.3", fc="cyan", ec="b", lw=2, shadow=True)
arrow_props = dict(arrowstyle="->")

ax.annotate('How2matplotlib.com', (2, 4), xytext=(3, 6),
             bbox=bbox_props, arrowprops=arrow_props)

plt.show()

In this example, we have added a shadow effect to the annotation box.

Annotation Box with Text Rotation

You can rotate the text in the annotation box by setting the rotation property. Here’s an example:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [1, 4, 9, 16])

bbox_props = dict(boxstyle="round,pad=0.3", fc="cyan", ec="b", lw=2)
arrow_props = dict(arrowstyle="->")

ax.annotate('How2matplotlib.com', (2, 4), xytext=(3, 6),
             bbox=bbox_props, arrowprops=arrow_props, rotation=45)

plt.show()

Output:

In this example, we have rotated the text in the annotation box by 45 degrees.

Annotation Box with Text Alignment

You can align the text in the annotation box to the left, right, or center. Here’s an example of right-aligned text:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [1, 4, 9, 16])

bbox_props = dict(boxstyle="round,pad=0.3", fc="cyan", ec="b", lw=2)
arrow_props = dict(arrowstyle="->")

ax.annotate('How2matplotlib.com', (2, 4), xytext=(3, 6),
             bbox=bbox_props, arrowprops=arrow_props, ha='right')

plt.show()

Output:

In this example, we have right-aligned the text in the annotation box.

Annotation Box with Text Font

You can change the font of the text in the annotation box by setting the font properties. Here’s an example:

import matplotlib.pyplot as plt
from matplotlib.font_manager import FontProperties

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [1, 4, 9, 16])

font = FontProperties()
font.set_family('serif')
font.set_style('italic')

bbox_props = dict(boxstyle="round,pad=0.3", fc="cyan", ec="b", lw=2)
arrow_props = dict(arrowstyle="->")

ax.annotate('How2matplotlib.com', (2, 4), xytext=(3, 6),
             bbox=bbox_props, arrowprops=arrow_props, fontproperties=font)

plt.show()

Output:

In this example, we have changed the font of the text in the annotation box to a serif italic style.

Annotation Box with Text Background

You can add a background color to the text in the annotation box to highlight it. Here’s an example:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [1, 4, 9, 16])

bbox_props = dict(boxstyle="round,pad=0.3", fc="cyan", ec="b", lw=2)
arrow_props = dict(arrowstyle="->")

ax.annotate('How2matplotlib.com', (2, 4), xytext=(3, 6),
             bbox=bbox_props, arrowprops=arrow_props, textcoords='axes fraction',
             fontsize=12, family='monospace', backgroundcolor='lightyellow')

plt.show()

Output:

In this example, we have added a light yellow background color to the text in the annotation box.