This proportional symbols map visualizes the global distribution of MOOC subscribers, using a choropleth color scheme where darker reds indicate higher subscriber counts. The map uses a Mercator projection, rendered via `d3.geoPath` and `d3.geoMercator`, with data loaded from a CSV file containing country codes and totals. A `d3.scaleThreshold` color scale maps subscriber ranges to a red color scheme, and a legend created with `d3.legendColor` explains the thresholds. The geographic boundaries come from a GeoJSON world map.