This example displays a map of Japan rendered as SVG paths, with a slider controlling the level of topographic simplification. The visualization uses a TopoJSON dataset of Japan, which is converted to GeoJSON via `topojson.feature` and then processed with `topojson.presimplify` to compute area-based simplification weights. A `d3.geoTransform` custom stream applies a threshold filter, and `d3.geoPath` projects the filtered coordinates using a Mercator projection fitted to the viewport. The slider triggers redraws that dynamically show coarser or finer terrain detail, with a header reading “Japan Map.”