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Tan Y Lan Road

501.7 m · net rise 51.7 m · overall 10.3% · evidence quality B (good) · Bae Colwyn · Clwyd · share

Shape: sustained — 43% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 260 m.

Found purely from mapping and LiDAR data, and not yet matched against books, race records or lists — it may be well known to locals under a name we've never heard. It was cross-checked against the OS road network, surface models and map tags, but a discovery can still be an artifact of the terrain model or the map. Treat it as a well-evidenced hypothesis until someone has ridden it. If you know this road, tell us what you found — photographs, corrections and local knowledge all welcome; the map links below let you scout it first.

Gradient ladder what do windows mean?

may continue beyond end Extent detection suggests reviewing where this climb starts/ends.

Map

Check this route yourself: Google Maps route via their router · Street View at the base where coverage exists · geojson.io our exact measured line · OpenTopoMap

No aerial layer here: Britain has no open or government source of aerial photography at road scale — the pan-government APGB imagery is licensed to the public sector only, unlike the LiDAR this survey is measured from. Street View, where it exists, is the visual check.

This climb's data: OCL JSON — the full gradient ladder, quality flags and provenance in the OpenClimb Ladder format.

Access: Re-lined 2026-09-18 onto the road bed the Welsh Government's laser point cloud finds, and re-measured (Peter's ruling: our line was beside the road, not on it). The line moved at 1 points along the climb, by at most 4.0 m. On the new line the steepest 25 m falls 18.85 % (was 20.20 %). The new figure is below the 20 % ranking door, so the page is listed rather than ranked: kept for the record, at the honest number.

Measured, not vetted. This page records what the laser record shows about the road's shape — nothing more. Nobody has necessarily ridden or inspected this road for the survey, and a page here is not a recommendation and no guarantee that the road is open, surfaced, rideable or safe. Gates, private sections, missing rights of way and hazards do not show up in elevation data. Check access and conditions on the ground and make your own judgment.

Ridden it, or know better? Submit data for this climb no account needed · Share this climb

Load the interactive map

Route colour = gradient over a 25 m window: <10% 10–20% 20–25% ≥25%

Topo (contours) Vector   © OpenStreetMap contributors · topo tiles © OpenTopoMap (CC-BY-SA) · vector tiles OpenFreeMap

Profile

The map, profile and gradient chart share one position — move your pointer over them and the marker follows. Colors are the gradient bands; the shaded span is the steepest 25 m. Any 25 m figure is good to about a point either way (why).

 

Measurement card

Provenance

{
  "analysis_version": "0.1.0",
  "sample_interval_m": 1.0,
  "interpolation": "bilinear",
  "smoothing": "none",
  "gradient_windows_m": [
    5.0,
    10.0,
    20.0,
    25.0,
    50.0,
    100.0
  ],
  "diagnostic_windows_m": [
    2.0,
    3.0
  ],
  "elevation_crs": "EPSG:27700",
  "elevation_resolution_m": 1.0,
  "elevation_tiles": [
    "data/cache/wales/dtm_1m/wg_del_30_287378_20220320dtm.tif"
  ],
  "calculated_at": "2026-09-19T03:18:01+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",
  "run_id": "wales-remeasure-260918",
  "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_30_287378_20220320dtm.tif"
  ],
  "elevation_capture_dates": [
    "20-03-2022"
  ],
  "climb_origin": "discovered",
  "structure_own_ways": "none \u2014 the route carried no way list; own decks unmasked",
  "carriageway": {
    "stations": 27,
    "stations_resolved": 27,
    "width_median_m": 6.25,
    "width_p10_m": 3.65,
    "width_min_m": 3.25,
    "width_max_m": 11.5,
    "bounded_share": 0.074,
    "unbounded_share": 0.926,
    "confidence_median": 0.0,
    "width_median_bounded_m": 5.0,
    "window_m": [
      468.0,
      493.0
    ],
    "width_at_max25_m": 4.25,
    "window_stations": 7,
    "single_track": false,
    "single_track_rule": "PROVISIONAL (2026-09-15): width_p10_m <= 3.0 m with bounded_share >= 0.6; recorded, not a rule",
    "status": "ok",
    "source": "dtm",
    "station_m": 25.0,
    "window_station_m": 5.0,
    "halfwidth_m": 6.0,
    "step_m": 0.25,
    "level_tol_m": 0.12,
    "break_min_m": 0.3,
    "stations_failed": 0,
    "hedge_to_hedge": {
      "stations": 27,
      "stations_resolved": 27,
      "width_median_m": 7.0,
      "width_p10_m": 3.05,
      "width_min_m": 2.25,
      "width_max_m": 12.0,
      "bounded_share": 0.741,
      "unbounded_share": 0.259,
      "confidence_median": 1.0,
      "width_median_bounded_m": 5.88,
      "window_m": [
        468.0,
        493.0
      ],
      "width_at_max25_m": 5.75,
      "window_stations": 7,
      "status": "ok",
      "source": "dsm",
      "station_m": 25.0,
      "window_station_m": 5.0,
      "halfwidth_m": 6.0,
      "step_m": 0.25,
      "level_tol_m": 0.5,
      "break_min_m": 0.3,
      "stations_failed": 0
    }
  },
  "door_status": "below every adoption door at fold time \u2014 kept pending: a published page falling below the door after an honest re-measure keeps its page and is LISTED, not ranked (the 2026-09-15 Welsh re-lines' own treatment); only Peter's explicit word retires a published page",
  "license": "ODbL-1.0",
  "license_url": "https://howsteep.org/licensing"
}