This example displays a choropleth of Japan, rendered as an SVG path using the d3.geoPath projection. The visualization shows the country’s terrain, dynamically simplified based on a user-adjusted threshold slider, which filters out triangular areas below the set value. Built with d3.v4 and topojson, it loads GeoJSON data from a remote GitHub source and re-renders the map on slider input or window resize, using the d3.geoTransform for custom simplification.