Prenteg to Cwm Ystradllyn°
4444.8 m · net rise 191.2 m · total ascent 276.0 m · overall 4.3% · confidence: good · Prenteg · Gwynedd
Shape: stepped — 58% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 283 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.
° The name is provisional: this climb is not yet matched to a documented name, so it was named from nearby map places. There is no evidence of local usage — (auto-named from gazetteer (hypothesis, unreviewed); discovered as 'Discovered lane (52.9531, -4.1311)'). Corrections welcome.
≈ 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) | ≈46% | 1743–1745 m | under overhead cover terrain reads 60.3% at 435–437 m across a structure — excluded |
| 3 m (diagnostic) | ≈40% | 1743–1746 m | under overhead cover terrain reads 48.5% at 434–437 m across a structure — excluded |
| 5 m | ≈35% | 1741–1746 m | under overhead cover terrain reads 44.4% at 432–437 m across a structure — excluded |
| 10 m | ≈28% | 1740–1750 m | under overhead cover terrain reads 34.5% at 428–438 m across terrain that holds no road surface (dense canopy, no bench) — excluded |
| 20 m | 25.1% | 1740–1760 m | |
| 25 m | 24.7% | 1740–1765 m | |
| 50 m | 21.8% | 1720–1770 m | |
| 100 m | 19.9% | 1711–1811 m |
descends_at_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
© OpenStreetMap contributors · topo tiles © OpenTopoMap (CC-BY-SA) · vector tiles OpenFreeMap
Profile
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_23_255342_20220111dtm.tif",
"data/cache/wales/dtm_1m/wg_del_23_256342_20220111dtm.tif",
"data/cache/wales/dtm_1m/wg_del_23_257342_20220111dtm.tif",
"data/cache/wales/dtm_1m/wg_del_23_258342_20220111dtm.tif",
"data/cache/wales/dtm_1m/wg_del_27_255341_20220111dtm.tif",
"data/cache/wales/dtm_1m/wg_del_27_256341_20220111dtm.tif",
"data/cache/wales/dtm_1m/wg_del_27_257341_20220111dtm.tif",
"data/cache/wales/dtm_1m/wg_del_27_258341_20220111dtm.tif"
],
"calculated_at": "2026-08-12T00:53:20+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_23_255342_20220111dtm.tif",
"wg_del_23_256342_20220111dtm.tif",
"wg_del_23_257342_20220111dtm.tif",
"wg_del_23_258342_20220111dtm.tif",
"wg_del_27_255341_20220111dtm.tif",
"wg_del_27_256341_20220111dtm.tif",
"wg_del_27_257341_20220111dtm.tif",
"wg_del_27_258341_20220111dtm.tif"
],
"elevation_capture_dates": [
"11-01-2022",
"17-01-2022"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 17.1% over 200 m (Terrain 50), gain 144.8 m over 4097 m way. EXTENDED by graph walk: +3 segment(s) at base, +0 at top (stop: base=no_descending_continuation, top=no_ascending_continuation; min_avg=2.0%). Review before adopting. DEDUPE: absorbed 2 overlapping proposal(s): discovered-lane-52-9526-4-1076, discovered-lane-52-9566-4-1183",
"naming_note": "auto-named from gazetteer (hypothesis, unreviewed); discovered as 'Discovered lane (52.9531, -4.1311)'"
}