How to Position Legends Inside a Plot in Plotly-Python?

Plotly-Python is a powerful visualization library that allows data scientists to create interactive plots with customizable legends. By default, Plotly positions legends outside the plot area, but positioning them inside can improve aesthetics, save space, and enhance the overall user experience.

In this guide, we'll explore different methods for positioning legends inside plots using Plotly-Python's layout.legend property and coordinate system.

Understanding Legend Positioning

Legends in Plotly use a coordinate system where values range from 0 to 1. The coordinates (0, 0) represent the bottom-left corner, while (1, 1) represents the top-right corner of the plot area. This system allows precise control over legend placement.

Basic Legend Positioning

To position a legend inside the plot, use the layout.legend property with x and y coordinates ?

import plotly.graph_objects as go

# Sample data
x_values = [1, 2, 3, 4, 5]
y_values1 = [2, 4, 1, 5, 3]
y_values2 = [1, 3, 2, 4, 5]

# Create traces
trace1 = go.Scatter(x=x_values, y=y_values1, name='Dataset A', mode='markers')
trace2 = go.Scatter(x=x_values, y=y_values2, name='Dataset B', mode='lines')

# Create figure and position legend inside
fig = go.Figure([trace1, trace2])
fig.update_layout(legend=dict(x=0.7, y=0.9))

fig.show()

This positions the legend in the upper-right area of the plot (x=0.7, y=0.9).

Using Anchor Properties for Better Control

The xanchor and yanchor properties provide better control over legend alignment, especially for different plot sizes ?

import plotly.graph_objects as go

# Sample data
x_values = [1, 2, 3, 4, 5]
y_values1 = [2, 4, 1, 5, 3]
y_values2 = [1, 3, 2, 4, 5]

# Create traces
trace1 = go.Scatter(x=x_values, y=y_values1, name='Dataset A', mode='markers')
trace2 = go.Scatter(x=x_values, y=y_values2, name='Dataset B', mode='lines')

# Create figure with anchored legend
fig = go.Figure([trace1, trace2])
fig.update_layout(
    legend=dict(
        x=0.02,
        y=0.98,
        xanchor='left',
        yanchor='top'
    )
)

fig.show()

This positions the legend at the top-left corner with proper anchoring for consistent placement across different plot sizes.

Legend Positioning in Subplots

When working with subplots, you can position legends inside each subplot area ?

import plotly.graph_objects as go
from plotly.subplots import make_subplots

# Sample data
x_values = [1, 2, 3, 4, 5]
y_values1 = [2, 4, 1, 5, 3]
y_values2 = [1, 3, 2, 4, 5]

# Create subplots
fig = make_subplots(
    rows=1, cols=2, 
    subplot_titles=('Plot A', 'Plot B'),
    horizontal_spacing=0.1
)

# Add traces to subplots
fig.add_trace(
    go.Scatter(x=x_values, y=y_values1, name='Series 1', mode='markers'),
    row=1, col=1
)
fig.add_trace(
    go.Scatter(x=x_values, y=y_values2, name='Series 2', mode='lines'),
    row=1, col=2
)

# Position legend inside subplot area
fig.update_layout(
    legend=dict(
        x=0.5,
        y=0.15,
        xanchor='center',
        yanchor='bottom',
        orientation='h'
    )
)

fig.show()

The orientation='h' parameter displays the legend horizontally, which works well at the bottom of subplot arrangements.

Common Legend Positions

Conclusion

Positioning legends inside plots using Plotly-Python improves space utilization and visual appeal. Use coordinate values (0-1) with anchor properties for precise control, and consider horizontal orientation for subplot legends.