Sankey diagrams visualize flows between nodes with width proportional to quantity. Perfect for showing user journeys, energy flows, budget allocation, and any process where items move between states.

Creating a Sankey Diagram

import plotly.graph_objects as go

# Website user flow: Landing → Pages → Actions
fig = go.Figure(data=[go.Sankey(
    node=dict(
        pad=15,
        thickness=20,
        label=["Homepage", "Product Page", "About", "Cart", "Checkout", "Purchase"],
        color=["blue", "orange", "green", "yellow", "red", "purple"]
    ),
    link=dict(
        source=[0, 0, 0, 1, 1, 3, 4],  # From node indices
        target=[1, 2, 3, 3, 4, 4, 5],  # To node indices
        value=[1000, 300, 500, 400, 300, 600, 200]  # Flow quantities
    )
)])

fig.update_layout(title="Website User Journey", font=dict(size=12))
fig.show()

Common Use Cases

Budget Allocation

# Company budget flow from revenue to expenses
nodes = ["Revenue", "Operating Costs", "Marketing", "R&D",
         "Salaries", "Infrastructure", "Advertising", "Social Media"]

links = {
    'source': [0, 0, 0, 1, 2, 2],  # Revenue splits to three departments
    'target': [1, 2, 3, 4, 6, 7],
    'value': [500000, 200000, 300000, 400000, 100000, 100000]
}

# Shows where money flows through organization

Customer Journey

# Marketing channel → Landing page → Conversion
source: ["Facebook", "Google", "Email", "Facebook", "Google", "Email"]
target: ["Landing A", "Landing A", "Landing B", "Convert", "Convert", "Convert"]
value: [1000, 1500, 800, 150, 300, 120]

# Visualizes conversion funnel from multiple sources

Energy Flow

# Energy production → consumption
Production sources → Distribution → End uses
Coal/Gas/Solar → Grid → Residential/Industrial/Commercial

Width shows proportion of total energy

Sankey Best Practices

• Arrange nodes logically (left to right flow)
• Use distinct colors for different categories
• Show values on hover for exact numbers
• Limit to 15-20 nodes for readability
• Ensure all flows sum correctly

Multi-Level Sankey

import plotly.graph_objects as go

# Traffic source → Landing page → Action → Outcome
fig = go.Figure(data=[go.Sankey(
    arrangement='snap',
    node={
        'label': [
            # Sources
            'Organic', 'Paid', 'Social',
            # Landing pages
            'Home', 'Product', 'Blog',
            # Actions
            'Browse', 'Add to Cart', 'Purchase'
        ],
        'color': ['#1f77b4'] * 3 + ['#ff7f0e'] * 3 + ['#2ca02c'] * 3
    },
    link={
        'source': [0,0,1,1,2,2, 3,3,4,4,5,5, 6,7,7],
        'target': [3,4,4,5,3,5, 6,7,6,7,6,8, 7,8,8],
        'value':  [500,300,400,200,300,100, 400,200,300,300,200,100, 100,150,250]
    }
)])

fig.update_layout(title="Multi-Stage User Journey")
fig.show()

When to Use Sankey Diagrams

• Showing flows between categories
• Visualizing proportional splits
• Tracking user journeys
• Budget/resource allocation
• Supply chain visualization