This interactive stream graph visualizes the median property prices in Massachusetts over time, allowing users to toggle between coloring by property type (house or unit) and by number of bedrooms (1–5). The D3.js v4 code uses `d3.stack`, `d3.stackOffsetSilhouette`, and `d3.area` to render the layered areas from a CSV file of quarterly sales data. Users switch coloring modes via buttons, which re-organize the data with `d3.nest` and recalculate medians before redrawing the SVG. Hovering over the graph reveals details through a tooltip element.