This interactive dashboard visualizes COVID-19 case distributions across Beijing districts using a coordinated histogram and pie chart. Hovering over a bar filters the pie chart and legend to show the selected district’s breakdown by infection source, including categories like Chaoyang, Haidian, and imported cases. Built with D3 v3, the example uses d3.svg.axis, ordinal and linear scales, and transition().duration() to animate bar height and color changes, while SVG paths render the interactive pie slices.