This interactive map displays Japan’s districts, rendered as colored SVG paths that highlight region names on hover via tooltips. Built with D3 v4 and TopoJSON, it uses a Mercator projection and a custom `d3.geoTransform` to apply topology-preserving simplification controlled by a range slider, redrawing the map dynamically. The initial data comes from the deldersveld TopoJSON repository, with fill colors changing from LightSkyBlue to Maroon on mouseout.