A dropdown menu filters a COVID-19 dataset by location, displaying two time-series lines for total cases and total deaths over date. The chart uses d3.axisBottom, d3.axisLeft, and d3.line to render axes and paths, with a tooltip that appears on mouseover using d3.bisector. Interactivity is managed via a location selector and event listeners, drawing from cleaned_covid_data.csv and rendering in SVG.