BETA — measurements and names under active refinement. Seen a sign, a gate, or a better name? Report it (photos welcome).

Devil's Staircase

841.5 m · gain 111.1 m · overall 13.2% · Coed Nant-yr-hwch · Powys

Shape: sustained — 36% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 243 m.

Known from: Another 100 Greatest Cycling Climbs (Simon Warren).

≈ Overhead cover (tree canopy or structures) spans 8% 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, not wrong. Longer windows average over more clean ground and are steadier.

Gradient ladder what do windows mean?

Window	Maximum	Located at
2 m (diagnostic)	37.3%	322–324 m
3 m (diagnostic)	36.0%	321–324 m
5 m	29.0%	443–448 m
10 m	26.8%	308–318 m
20 m	24.7%	308–328 m
25 m	24.5%	375–400 m
50 m	23.0%	347–397 m
100 m	22.5%	307–407 m

may_start_earliermay_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

Devil's Staircase LiDAR hillshade map with contours

Profile

Reported values vs. measurement

Source	Claim	Evidence	Best-matching window
Road sign / OSM incline tag	25%	road_sign	20 m (+0.3 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_22_282255_20220114dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_22_282256_20220114dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_26_283255_20220226dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_26_283256_20220226dtm.tif"
  ],
  "calculated_at": "2026-08-12T09:11:49+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_22_282255_20220114dtm.tif",
    "wg_del_22_282256_20220114dtm.tif",
    "wg_del_26_283255_20220226dtm.tif",
    "wg_del_26_283256_20220226dtm.tif"
  ],
  "elevation_capture_dates": [
    "14-01-2022",
    "26-02-2022"
  ],
  "climb_origin": "named",
  "signed_gradient_pct": 25,
  "signed_source": "OSM incline tag (25%)",
  "notes": "Abergwesyn pass, hairpinned section. Famous audax/sportive climb. EXTENDED by graph walk: +1 segment(s) at base, +0 at top (stop: base=no_descending_continuation, top=no_ascending_continuation; min_avg=2.0%). Review before adopting."
}