This chart displays New York's homeless population from 2009 to 2012, breaking down counts by borough (Manhattan, Bronx, etc.) and by location category (Surface, Subways, Total Unsheltered) for each year. The data is read from a CSV file using `d3.csv`, and bars are rendered in SVG using `scaleBand`, `scaleLinear`, and `scaleOrdinal` for positioning and color coding by year. Axes are added with `axisLeft` and `axisBottom`, and a color legend distinguishes the four years.