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Twtil

352.2 m · net rise 49.5 m · overall 14.1% · confidence: good · Harlech · Gwynedd

Shape: sustained — 32% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 294 m.

Documented on the ground — tag: 25% (2026). Signs get repainted and tags get retagged, so the date is part of the fact; not yet matched against any cycling list.

≈ Overhead cover (tree canopy or structures) spans 9% of this route — detected by comparing the surface model (DSM, treetops and rooftops) against the terrain model (DTM, bare ground). Under cover the bare-ground model is built from fewer laser returns, so metre-scale readings can wobble; maxima whose window sits in a covered zone are marked ≈ below — less certain — the flag does not say whether the true value is higher or lower. Longer windows average over more clean ground and are steadier.

Gradient ladder what do windows mean?

Window	Maximum	Located at
2 m (diagnostic)	≈29%	261–263 m	under overhead cover terrain reads 87.2% at 347–349 m across a structure — excluded
3 m (diagnostic)	≈29%	261–264 m	under overhead cover terrain reads 74.8% at 347–350 m across a structure — excluded
5 m	≈25%	259–264 m	under overhead cover terrain reads 46.8% at 346–351 m across a structure — excluded
10 m	≈23%	124–134 m	under overhead cover terrain reads 24.7% at 340–350 m across a structure — excluded
20 m	21.9%	115–135 m
25 m	21.5%	111–136 m
50 m	19.7%	97–147 m
100 m	17.2%	202–302 m

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

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

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

Profile

Reported values vs. measurement

Source	Claim	Evidence	Best-matching window
OSM incline tag	25%	mapper_estimate	5 m (-0.0 pp)

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_27_258331_20220111dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_30_257331_20220320dtm.tif"
  ],
  "calculated_at": "2026-08-12T09:11:50+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",
    "wg_del_30_257331_20220320dtm.tif"
  ],
  "elevation_capture_dates": [
    "11-01-2022",
    "20-03-2022"
  ],
  "climb_origin": "osm_incline",
  "notes": "Harlech, neighbour of Ffordd Pen Llech. EXTENDED by graph walk: +0 segment(s) at base, +6 at top (stop: base=no_descending_continuation, top=no_ascending_continuation; min_avg=2.0%). Review before adopting."
}