How to Create a Population Pyramid Using Plotly in Python?

A population pyramid is a graphical representation of the age and gender distribution of a population. It consists of two back-to-back bar charts, one showing the distribution of males and the other showing the distribution of females across different age groups. The population pyramid is a powerful visualization tool that can help us understand the demographic composition of a population and identify trends and patterns.

In this article, we will explore how to create a population pyramid using Plotly in Python. Plotly is a powerful visualization library that allows us to create interactive and dynamic plots in Python.

We will use Plotly to create a population pyramid that shows the age and gender distribution of a population. We will start by creating sample data and then use Plotly to create the population pyramid.

Using Plotly Express

Plotly Express is a high-level API for Plotly that makes it easy to create many types of plots, including population pyramids. We can use the px.bar() function to create the two back-to-back bar charts that make up the population pyramid.

Example

import plotly.express as px
import pandas as pd

# Create sample population data
age_groups = ['0-9', '10-19', '20-29', '30-39', '40-49', '50-59', '60-69', '70+']
male_counts = [1200, 1500, 1800, 1600, 1400, 1200, 800, 400]
female_counts = [1100, 1400, 1700, 1550, 1350, 1150, 850, 500]

# Create DataFrame
df = pd.DataFrame({
    'age': age_groups + age_groups,
    'count': male_counts + female_counts,
    'gender': ['Male'] * len(age_groups) + ['Female'] * len(age_groups)
})

# Adjust female counts to negative for pyramid effect
df.loc[df['gender'] == 'Female', 'count'] *= -1

# Create the population pyramid using Plotly Express
fig = px.bar(df, x="count", y="age", orientation="h", color="gender",
             barmode="relative", 
             title="Population Pyramid",
             labels={'count': 'Population Count', 'age': 'Age Group'})

# Update layout for better visualization
fig.update_layout(xaxis_title="Population Count")

# Show the plot
fig.show()

Explanation

• We start by importing the libraries, including plotly.express for creating the plot and pandas for creating the DataFrame.

• We create sample population data with age groups and corresponding counts for males and females.

• We construct a DataFrame with age groups, counts, and gender information.

• Female counts are multiplied by -1 to create the pyramid effect where females appear on the left side.

• The px.bar() function creates the pyramid with horizontal orientation and relative bar mode.

• Finally, we display the plot using the show() method.

Using Plotly Graph Objects

Plotly Graph Objects is a lower-level API for Plotly that provides more flexibility and control over the plot layout and styling. We can use Plotly Graph Objects to create a population pyramid by creating two bar traces, one for males and the other for females, and then combining them into a single figure.

Example

import plotly.graph_objs as go
import pandas as pd

# Create sample population data
age_groups = ['0-9', '10-19', '20-29', '30-39', '40-49', '50-59', '60-69', '70+']
male_counts = [1200, 1500, 1800, 1600, 1400, 1200, 800, 400]
female_counts = [1100, 1400, 1700, 1550, 1350, 1150, 850, 500]

# Create the male bar trace
trace_male = go.Bar(x=male_counts,
                    y=age_groups,
                    orientation="h",
                    name="Male",
                    marker=dict(color="#1f77b4"))

# Create the female bar trace (negative values for left side)
trace_female = go.Bar(x=[-count for count in female_counts],
                      y=age_groups,
                      orientation="h",
                      name="Female",
                      marker=dict(color="#d62728"))

# Create the layout
layout = go.Layout(title="Population Pyramid",
                   xaxis=dict(title="Population Count"),
                   yaxis=dict(title="Age Group"),
                   barmode="overlay",
                   bargap=0.1)

# Create the figure
fig = go.Figure(data=[trace_male, trace_female], layout=layout)

# Show the plot
fig.show()

Explanation

• We import plotly.graph_objs and pandas for creating the plot and handling data.

• Sample population data is created with age groups and counts for both genders.

• Two bar chart traces are created using go.Bar() - one for males and one for females.

• Female counts are converted to negative values to create the left side of the pyramid.

• A layout is created with title and axis labels using go.Layout().

• The figure is created by combining both traces with the layout using go.Figure().

• Finally, the plot is displayed using fig.show().

Comparison

Conclusion

Population pyramids are effective tools for visualizing demographic data. Plotly Express offers a quick solution for basic pyramids, while Graph Objects provides more control for custom styling and advanced features.