The visualization displays the number of new HIV cases per quarter across 50 districts, shown as layered line and circle marks. Users interact with a React-Select multi-select dropdown to filter which districts appear, with the chart updating dynamically. The code uses Vega-Lite API to build the layered specification, D3.js to load CSV data from a GitHub gist, and React for state management and re-rendering. Tooltips are enabled through Vega-Tooltip, while the chart’s size adapts to the window dimensions.