This visualization displays monthly出入境 (immigration and emigration) passenger totals across 29 Taiwanese airports and harbors from 2015 onward, using a multi-line chart. Users toggle individual locations via checkboxes to add or remove their corresponding time-series lines, while a shared y-axis scales dynamically to the selected data range. The chart is built with D3 v5, using `d3.scaleTime` and `d3.line` for path generation, `d3.axisBottom` and `d3.axisLeft` for axes, and SVG rendering.