This stacked bar chart visualizes the age distribution of illness cases across Chinese provinces, with each bar segmented into ten-year age brackets from 0-10 to 90-100 years. Users can toggle between raw case counts and percentage-of-illness views via radio buttons. Built with D3.js version 3.5, the visualization uses `d3.layout.stack` for stacking, `d3.scale.ordinal` and `d3.scale.linear` for axes, and includes smooth transitions when switching between count and percent modes. The data comes from a CSV file, with SVG rendering and interactive hover effects.