都道府県判定データ
Source: https://github.com/piuccio/open-data-jp-prefectures-geojson
Original: 国土数値情報 行政区域データ
ヨリマルではmapshaperで1%に簡略化（keep-shapes、精度0.0001度）。県境・海岸付近の判定は概略です。
取得日: 2026-10-18

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