{
  "generatedDate": "2026-10-17",
  "credit": "地図：国土地理院 / 国土数値情報（加工）",
  "sources": [
    {
      "name": "SmartNews Media Research Institute japan-topography",
      "url": "https://github.com/smartnews-smri/japan-topography",
      "datasetUrl": "https://raw.githubusercontent.com/smartnews-smri/japan-topography/main/data/municipality/geojson/s0010/prefectures.json",
      "underlyingSource": "MLIT National Land Numerical Information administrative areas; 2021 source acquired by processor 2021-09-28",
      "bytes": 2384869,
      "sha256": "234914ee3a13beea6ef25f148e5c3a1ba6d0d1f0d0d8eb2af6a1732792ecf3ed",
      "httpStatus": 200,
      "corsAllowOrigin": "*"
    },
    {
      "name": "MLIT National Land Numerical Information terms",
      "url": "https://nlftp.mlit.go.jp/ksj/other/agreement_01.html",
      "notice": "国土数値情報（行政区域）を加工して作成。2021年由来の簡略化済み表示用データであり、最新の測量成果を示すものではありません。"
    },
    {
      "name": "GSI optimized vector basemap",
      "url": "https://github.com/gsi-cyberjapan/optimal_bvmap",
      "pmtilesUrl": "https://cyberjapandata.gsi.go.jp/xyz/optimal_bvmap-v1/optimal_bvmap-v1.pmtiles",
      "terms": "https://www.gsi.go.jp/kikakuchousei/kikakuchousei40182.html",
      "notice": "国土地理院最適化ベクトルタイルを加工。Only runtime byte ranges are fetched; no archive is bundled."
    },
    {
      "name": "GSI Japanese glyphs",
      "url": "https://gsi-cyberjapan.github.io/optimal_bvmap/glyphs/{fontstack}/{range}.pbf",
      "testedUrl": "https://gsi-cyberjapan.github.io/optimal_bvmap/glyphs/NotoSansJP-Regular/19968-20223.pbf",
      "httpStatus": 200,
      "corsAllowOrigin": "*"
    },
    {
      "name": "GSI seamless aerial photography and satellite mosaic for real mode",
      "url": "https://maps.gsi.go.jp/development/ichiran.html#seamlessphoto",
      "terms": "https://www.gsi.go.jp/kikakuchousei/kikakuchousei40182.html",
      "tileTemplate": "https://cyberjapandata.gsi.go.jp/xyz/seamlessphoto/{z}/{x}/{y}.jpg",
      "tileSize": 256,
      "minzoom": 2,
      "maxzoom": 18,
      "checkedAt": "2026-10-19",
      "notice": "国土地理院の写真をリアルタイム表示。日本以外をマスクし、行政境界・地名・アニメ地点を重ねて表示する加工。写真そのものの色は変えません。撮影時期と解像度は地域・ズームにより異なります。",
      "zoomSources": [
        {
          "zoom": "2–8",
          "name": "世界衛星モザイク画像",
          "additionalCredit": "Images on 世界衛星モザイク画像 obtained from site https://lpdaac.usgs.gov/data_access maintained by the NASA Land Processes Distributed Active Archive Center (LP DAAC), USGS/Earth Resources Observation and Science (EROS) Center, Sioux Falls, South Dakota.",
          "dateQualification": "画像ごとの撮影年は未取得。確認日を撮影年として使わない。"
        },
        {
          "zoom": "9–13",
          "name": "全国ランドサットモザイク画像",
          "additionalCredit": "データソース：Landsat8画像（GSI,TSIC,GEO Grid/AIST）, Landsat8画像（courtesy of the U.S. Geological Survey）, 海底地形（GEBCO）"
        },
        {
          "zoom": "14–18",
          "name": "全国最新写真（シームレス）",
          "additionalCredit": "一部のGRUS画像：GRUS画像（© Axelspace）",
          "grusBounds": [
            136.066111,
            20.407778,
            136.140278,
            20.455833
          ]
        }
      ],
      "testedTiles": [
        {
          "url": "https://cyberjapandata.gsi.go.jp/xyz/seamlessphoto/4/14/6.jpg",
          "status": 200,
          "contentType": "image/jpeg",
          "bytes": 35310
        },
        {
          "url": "https://cyberjapandata.gsi.go.jp/xyz/seamlessphoto/9/454/201.jpg",
          "status": 200,
          "contentType": "image/jpeg",
          "bytes": 102825
        },
        {
          "url": "https://cyberjapandata.gsi.go.jp/xyz/seamlessphoto/14/14550/6451.jpg",
          "status": 200,
          "contentType": "image/jpeg",
          "bytes": 23279
        },
        {
          "url": "https://cyberjapandata.gsi.go.jp/xyz/seamlessphoto/18/232815/103222.jpg",
          "status": 200,
          "contentType": "image/jpeg",
          "bytes": 20401
        }
      ],
      "verificationQualification": "調査担当が公開タイル4枚を実取得して確認。全国の全タイル・全地域の可用性検証を意味しない。"
    },
    {
      "name": "GSI Japan extreme coordinates",
      "url": "https://www.gsi.go.jp/KOKUJYOHO/center.htm",
      "use": "Official Okinotorishima control point; marine visibility window only."
    },
    {
      "name": "孀婦岩 official coordinate",
      "url": "https://www1.kaiho.mlit.go.jp/kaiikiDB/kaiyo17-2.htm",
      "use": "Official island coordinate used only for a 2 km marine mask window."
    },
    {
      "name": "須美寿島 official coordinate",
      "url": "https://ds.data.jma.go.jp/vois/data/tokyo/324_Sumisujima/324_index.html",
      "use": "Official island coordinate used only for a 2 km marine mask window."
    },
    {
      "name": "ベヨネース列岩 official coordinate",
      "url": "https://www.data.jma.go.jp/vois/data/tokyo/323_BeyonesuRocks/323_index.html",
      "use": "Official island coordinate used only for a 2 km marine mask window."
    }
  ],
  "processing": {
    "library": "Shapely 2.1.2",
    "prefectures": "Exact s0010 source bytes, all 47 features and all source islands retained.",
    "labels": "polylabel on the largest component per prefecture, tolerance 0.003 degree, six-decimal output; hand-assigned collision priorities only.",
    "boundaries": "unary_union of feature boundaries minus the dissolved national boundary; shared lines simplify at 0.00002 degree and coast at 0.0001 degree. Round to six decimals and discard two zero-length remnants of floating-point intersections.",
    "mask": "Dissolve all 47 prefectures; use each island exterior with inland water retained. Project each island to spherical Mercator R=6378137 m, buffer 2000/cos(centroid latitude) projected meters with quad_segs=8, simplify 35/cos(latitude) meters with topology preservation, inverse-project, dissolve windows and retain enclosed interior water. Subtract windows from world rectangle [-180,-90,180,90], orient exterior counterclockwise and holes clockwise, round to six decimals. No convex hull.",
    "marineBufferMeters": 2000,
    "bufferDistanceQualification": "Ground distance is approximately 2 km and varies slightly over large islands because the scale is evaluated at the island centroid.",
    "sourceLandIntersectingFinalMaskSquareDegrees": 0.0,
    "sourceIslandCountAfterDissolve": 690,
    "maskHoleCount": 129,
    "remoteIslandWindows": [
      {
        "name": "Okinotorishima",
        "reason": "Omitted by the s0010 simplification; this opens the mask only and does not draw substitute island geography.",
        "source": "https://maps.gsi.go.jp/development/ichiran.html",
        "sourceSection": "GSI seamless-photo GRUS coverage bounds",
        "officialBounds": [
          136.066111,
          20.407778,
          136.140278,
          20.455833
        ],
        "bufferMeters": 2000,
        "officialSouthernmostPointSource": "https://www.gsi.go.jp/KOKUJYOHO/center.htm",
        "officialSouthernmostPoint": [
          136.069722,
          20.425278
        ]
      },
      {
        "name": "Sofugan",
        "nameJa": "孀婦岩",
        "officialPoint": [
          140.341944,
          29.794167
        ],
        "source": "https://www1.kaiho.mlit.go.jp/kaiikiDB/kaiyo17-2.htm",
        "bufferMeters": 2000,
        "reason": "Isolated small rock omitted by s0010 simplification. This changes only the visibility mask; GSI supplies all visible island geometry."
      },
      {
        "name": "Sumisujima",
        "nameJa": "須美寿島",
        "officialPoint": [
          140.050556,
          31.439722
        ],
        "source": "https://ds.data.jma.go.jp/vois/data/tokyo/324_Sumisujima/324_index.html",
        "bufferMeters": 2000,
        "reason": "Isolated small rock omitted by s0010 simplification. This changes only the visibility mask; GSI supplies all visible island geometry."
      },
      {
        "name": "Bayonnaise Rocks",
        "nameJa": "ベヨネース列岩",
        "officialPoint": [
          139.917778,
          31.888056
        ],
        "source": "https://www.data.jma.go.jp/vois/data/tokyo/323_BeyonesuRocks/323_index.html",
        "bufferMeters": 2000,
        "reason": "Isolated small rock omitted by s0010 simplification. This changes only the visibility mask; GSI supplies all visible island geometry."
      }
    ],
    "cameraBounds": "Initial fit excludes tiny remote islands only for legibility; source geography and mask preserve them.",
    "geographyQualification": "The exact 47-feature source is retained without relocation or distortion, including its jurisdictional conventions; it is a 2021-derived simplified administrative dataset, not an exhaustive current coastline survey. Remote source simplification omissions identified in targeted checks receive official-coordinate visibility windows. Current detailed visible geography comes from GSI."
  },
  "assets": [
    {
      "file": "japan-prefectures.geojson",
      "url": "/maps/japan-prefectures.geojson",
      "purpose": "47-prefecture overview; unchanged source file with all source islands",
      "bytes": 2384869,
      "sha256": "234914ee3a13beea6ef25f148e5c3a1ba6d0d1f0d0d8eb2af6a1732792ecf3ed"
    },
    {
      "file": "japan-prefecture-labels.geojson",
      "url": "/maps/japan-prefecture-labels.geojson",
      "purpose": "Labels derived from the largest polygon of each prefecture",
      "bytes": 7234,
      "sha256": "64215dc82b622118f873804760c0e1a022917782ec91e44aa513a842128662f1"
    },
    {
      "file": "japan-boundaries.geojson",
      "url": "/maps/japan-boundaries.geojson",
      "purpose": "Separate shared-prefecture borders and dissolved coastline",
      "bytes": 1413592,
      "sha256": "8138b33501f36706e02cb47592c58495f2aa7e4d72afb9c76f91c79a4395b0b1"
    },
    {
      "file": "japan-mask.geojson",
      "url": "/maps/japan-mask.geojson",
      "purpose": "Inverse world mask with approximately 2 km marine buffers and official remote-island visibility windows",
      "bytes": 624234,
      "sha256": "e69734449853db89a3f7f1242d772a005dac2af80d65cf8400e651f10b4e3efe"
    }
  ],
  "updatedAt": "2026-10-19"
}