The visualization shows the number of flight routes per airline as a horizontal bar chart, ranked by route count. Hovering over a bar highlights that airline and displays its flight routes on a world map using `d3.geoNaturalEarth1` projection with `d3.geoPath` for geographic rendering. The map draws airport connections as lines based on route data from the CSV file, while the bar chart uses `d3.scaleBand` and `d3.scaleLinear` for axes. The map background is rendered from GeoJSON country boundaries.