This example visualizes Japan’s population changes by prefecture from 1920 to 2012. A choropleth map colors each prefecture according to its population for a selected year, with a dropdown menu to switch years and an animated two-second color transition between selections. Capital cities are marked with circles using projected coordinates. The code uses d3.v3, queue, topojson, and d3-legend, applying d3.geo.mercator and d3.geo.path to render the map from TopoJSON data, while population data comes from the Statistics Bureau of Japan.