Dardy to Blaen Onneu°
6271.8 m · net rise 328.4 m · total ascent 360.7 m · overall 5.2% · confidence: good · Cwm Onnau · Powys
Shape: sustained — 38% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 318 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 (51.8555, -3.1826)'). Corrections welcome.
≈ Overhead cover (tree canopy or structures) spans 15% 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% | 1987–1989 m | under overhead cover terrain reads 91.5% at 8–10 m across a structure — excluded |
| 3 m (diagnostic) | ≈35% | 1986–1989 m | under overhead cover terrain reads 82.0% at 8–11 m across a structure — excluded |
| 5 m | ≈29% | 107–112 m | under overhead cover terrain reads 65.2% at 6–11 m across a structure — excluded |
| 10 m | ≈25% | 106–116 m | under overhead cover terrain reads 41.0% at 6–16 m across a structure — excluded |
| 20 m | ≈23.9% | 93–113 m | under overhead cover terrain reads 29.5% at 6–26 m across a structure — excluded |
| 25 m | ≈23.2% | 88–113 m | under overhead cover terrain reads 27.6% at 6–31 m across a structure — excluded |
| 50 m | ≈22.5% | 64–114 m | under overhead cover terrain reads 23.8% at 6–56 m across a structure — excluded |
| 100 m | ≈21.2% | 173–273 m | under overhead cover terrain reads 22.9% at 5–105 m across a structure — excluded |
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
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_20_315216_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_315217_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_315218_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_316216_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_316217_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_316218_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_317216_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_317217_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_317218_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_318216_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_318217_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_318218_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_319216_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_319217_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_319218_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_320216_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_320217_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_320218_20220112dtm.tif"
],
"calculated_at": "2026-08-12T09:07:15+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_20_315216_20220112dtm.tif",
"wg_del_20_315217_20220112dtm.tif",
"wg_del_20_315218_20220112dtm.tif",
"wg_del_20_316216_20220112dtm.tif",
"wg_del_20_316217_20220112dtm.tif",
"wg_del_20_316218_20220112dtm.tif",
"wg_del_20_317216_20220112dtm.tif",
"wg_del_20_317217_20220112dtm.tif",
"wg_del_20_317218_20220112dtm.tif",
"wg_del_20_318216_20220112dtm.tif",
"wg_del_20_318217_20220112dtm.tif",
"wg_del_20_318218_20220112dtm.tif",
"wg_del_20_319216_20220112dtm.tif",
"wg_del_20_319217_20220112dtm.tif",
"wg_del_20_319218_20220112dtm.tif",
"wg_del_20_320216_20220112dtm.tif",
"wg_del_20_320217_20220112dtm.tif",
"wg_del_20_320218_20220112dtm.tif"
],
"elevation_capture_dates": [
"12-01-2022"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 19.0% over 200 m (Terrain 50), gain 295.3 m over 5998 m way. 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. ADOPTED (notable slice 2026-08-11): big-gain. AUTO-NAMED from gazetteer (hypothesis, unreviewed): was 'Discovered lane (51.8555, -3.1826)'.",
"naming_note": "auto-named from gazetteer (hypothesis, unreviewed); discovered as 'Discovered lane (51.8555, -3.1826)'"
}