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How to Label Points on a Scatter Plot in Matplotlib?

In this tutorial, we will look at how to label points on a scatter plot in Matplotlib with the help of some examples.

How to annotate points on a scatter plot in matplotlib?

You can use the matplotlib.pyplot.text() function to label points in a matplotlib scatter plot. The matplotlib.pyplot.text() function is used to add text at the location (x, y) in the plot. The following is the syntax –

import matplotlib.pyplot as plt

# add text, s to a point at (x, y) coordinate in a plot
plt.text(x, y, s)

Now to add labels to each point in the scatter plot, use the matplotlib.pyplot.text() function for each point (x, y) and add its appropriate label.

Let’s now look at some examples of using the above syntax. First, we will create a simple scatter plot.

import matplotlib.pyplot as plt

# x values - years
x = [2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020]
# y values - 1 USD in INR
y = [46.67, 53.44, 56.57, 62.33, 62.97, 66.46, 67.79, 70.09, 70.39, 76.38]

# plot x and y on scatter plot
plt.scatter(x, y)

# add axes labels
plt.xlabel('Year')
plt.ylabel('1USD in INR')

Output:

scatter plot of year vs usd to rupee conversion data

Example 1 – Label a point on the scatter plot

In case you only want to label a specific point (or points), use the matplotlib.pyplot.text() function only for those points. For example, let’s label the point (2014, 62.33).

# plot x and y on scatter plot
plt.scatter(x, y)

# add axes labels
plt.xlabel('Year')
plt.ylabel('1USD in INR')

# add label to a point
plt.text(2014, 62.33, 'USD crosses\n60 Rupee mark')

Output:

a single point labelled on the scatter plot

You can customize the way the text label appears by using additional arguments. For example, you can adjust the vertical and the horizontal alignment of the text, you can rotate the text, etc.

# plot x and y on scatter plot
plt.scatter(x, y)

# add axes labels
plt.xlabel('Year')
plt.ylabel('1USD in INR')

# add label to a point
plt.text(2014, 62.33, 'USD crosses\n60 Rupee mark', va='center', ha='center')

Output:

shifted the label to center vertical and horizontal alignment.

Here, we used the va parameter to set the vertical alignment of the text to ‘center’ and the ha parameter to set the horizontal alignment to ‘center’ as well.

Example 2 – Label Each Point on the Scatter Plot

To label each point on the scatter plot, use the matplotlib.pyplot.text() function for each point in the plot.

# plot x and y on scatter plot
plt.scatter(x, y)

# add axes labels
plt.xlabel('Year')
plt.ylabel('1USD in INR')

# add labels to all points
for (xi, yi) in zip(x, y):
    plt.text(xi, yi, yi, va='bottom', ha='center')

Output:

all points in the scatter plot labelled with y value.

Here, we added the y-axis value of the point as its label for each point on the scatter plot.

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Author

  • Piyush Raj

    Piyush is a data professional passionate about using data to understand things better and make informed decisions. In the past, he's worked as a Data Scientist for ZS and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.