This Sankey diagram visualizes air pollution data from Geneva, showing the flow of pollutants between different categories and locations. The code loads CSV data from a GitHub gist and transforms it into a node-link structure using custom logic in `transformData`. It renders the diagram as an SVG using the D3.js v5 library, specifically leveraging the `d3.sankey()` layout to position nodes and links. Each link’s stroke opacity increases on hover, and nodes are colored using `d3.scaleOrdinal(d3.schemeCategory10)`.