This map visualizes population density across Maryland’s census tracts and counties, using a color scale from d3-scale-chromatic to show density values. The map also includes a draggable yellow circle marking Rockville, MD, whose position can be moved via d3.drag. The visualization loads TopoJSON tract boundaries and a separate population JSON, merges tracts into county outlines with topojson.merge, and projects the geometry using d3.geoConicConformal with fitSize. A tooltip shows coordinates on mousemove, while the SVG rendering relies on d3.geoPath and d3.queue.