都道府県マップ
This interactive choropleth map visualizes the number of buildings with basements constructed in each Japanese prefecture from 2011 to 2015, based on data from Japan’s e-Stat statistics portal. Users clickable legend labels switch between total counts and counts per basement floor level, each with 1-second animated color transitions. The map uses D3 v3’s `d3.geo.mercator`, `d3.geo.path`, and TopoJSON to render geographies, with zoom and pan via `d3.behavior.zoom`, plus a hover tooltip. A linear color scale encodes values from blue (low) to red (high). Tokyo, Osaka, and Hokkaido show notably higher counts.