This line graph displays the unsheltered homeless population in New York City from 2009 to 2012, broken down by borough and surface versus subway locations. The visualization is built with D3 v5, using `d3.scaleLinear` for axes, `d3.axisBottom` and `d3.axisLeft` for tick marks, and `d3.line` with `d3.curveBasis` to render the smooth paths. Data originates from a CSV file, and SVG is used for all rendering, with tooltips omitted.