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 "diagnostic_note": "Windows <=3 m are at raster-noise scale (1-sigma raster noise alone is roughly +/-7 pp at 2 m and +/-5 pp at 3 m on a 1 m DTM). Diagnostic use only: never a headline or ranking value.",
 "quality_summary": {
  "overhead_obstruction": {
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   "obstruction_max_height_m": 15.49,
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  "extent": [
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 },
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  "interpolation": "bilinear",
  "smoothing": "none",
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  "elevation_crs": "EPSG:27700",
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  "elevation_tiles": [
   "data/cache/wales/dtm_1m/wg_del_27_258331_20220111dtm.tif"
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  "calculated_at": "2026-08-12T09:11:48+00:00",
  "road_source": "OpenStreetMap (local PBF extract)",
  "road_attribution": "\u00a9 OpenStreetMap contributors, ODbL",
  "osm_pbf_path": "data/cache/pbf/wales-2026-08-11.osm.pbf",
  "osm_snapshot": "2026-08-10T20:21:40Z",
  "elevation_provider": "Welsh Government",
  "elevation_dataset": "Welsh Government LiDAR 1m DTM (2020-2023)",
  "elevation_licence": "Open Government Licence v3 \u2014 \u00a9 Crown copyright Welsh Government",
  "elevation_catalogue_layer": "geonode:welsh_government_lidar_tile_catalogue_2020_2023",
  "elevation_tile_ids": [
   "wg_del_27_258331_20220111dtm.tif"
  ],
  "elevation_capture_dates": [
   "11-01-2022"
  ],
  "climb_origin": "named",
  "notes": "One-way spiral street, Harlech. Guinness measured 37.45% at centreline-adjacent line in 2019; record returned to Baldwin St NZ after measurement-method dispute \u2014 exactly this project's subject. EXTENDED by graph walk: +1 segment(s) at base, +1 at top (stop: base=no_descending_continuation, top=no_ascending_continuation; min_avg=2.0%). Review before adopting."
 },
 "area": {
  "place": "Harlech",
  "county": "Gwynedd - Gwynedd"
 },
 "reported_claims": [
  {
   "source_name": "Road sign / OSM incline tag",
   "value_pct": 40,
   "evidence_type": "road_sign",
   "claimed_window_m": null,
   "description": "40% gradient warning signage, Harlech",
   "observation_date": "2010-08-06",
   "retrieved_at": "2026-08-10",
   "credibility": "Good: OSM incline=-40% stable since 2010; famous signed street",
   "observed_via": "osm_tag_history"
  },
  {
   "source_name": "Guinness World Records (2019)",
   "value_pct": 37.45,
   "evidence_type": "survey",
   "claimed_window_m": null,
   "source_url": "https://www.guinnessworldrecords.com/news/2019/7/harlech-street-in-wales-named-worlds-steepest",
   "description": "Measured for 'steepest street' record, later returned to Baldwin St NZ after a measurement-line/method dispute",
   "observation_date": "2019-07",
   "retrieved_at": "2026-08-10",
   "credibility": "Professional survey, but the measurement line and averaging distance were the disputed points \u2014 no explicit window"
  }
 ],
 "confidence": "B",
 "shape": {
  "ascent_concentration": 0.41,
  "concentration_window_frac": 0.25,
  "longest_pitch_10pct_m": 173.0,
  "shape_class": "sustained"
 }
}