Cyffredyn to Blaen Onneu°
4793.6 m · net rise 323.3 m · total ascent 339.2 m · overall 6.7% · confidence: good · Cwm Cleisfer · Powys
Shape: sustained — 33% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 112 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 (51.8486, -3.2344)'). Corrections welcome.
≈ Overhead cover (tree canopy or structures) spans 5% 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) | ≈30% | 2197–2199 m | under overhead cover |
| 3 m (diagnostic) | ≈28% | 2197–2200 m | under overhead cover |
| 5 m | ≈23% | 2197–2202 m | under overhead cover |
| 10 m | ≈20% | 2197–2207 m | under overhead cover |
| 20 m | 16.7% | 2078–2098 m | |
| 25 m | 16.2% | 2073–2098 m | |
| 50 m | 14.6% | 2048–2098 m | |
| 100 m | 12.9% | 1998–2098 m |
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_314216_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_314217_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_314218_20220112dtm.tif",
"data/cache/wales/dtm_1m/wg_del_20_314219_20220112dtm.tif",
"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_315219_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_316219_20220112dtm.tif"
],
"calculated_at": "2026-08-12T09:07:11+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_314216_20220112dtm.tif",
"wg_del_20_314217_20220112dtm.tif",
"wg_del_20_314218_20220112dtm.tif",
"wg_del_20_314219_20220112dtm.tif",
"wg_del_20_315216_20220112dtm.tif",
"wg_del_20_315217_20220112dtm.tif",
"wg_del_20_315218_20220112dtm.tif",
"wg_del_20_315219_20220112dtm.tif",
"wg_del_20_316216_20220112dtm.tif",
"wg_del_20_316217_20220112dtm.tif",
"wg_del_20_316218_20220112dtm.tif",
"wg_del_20_316219_20220112dtm.tif"
],
"elevation_capture_dates": [
"12-01-2022"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 11.1% over 200 m (Terrain 50), gain 324.1 m over 4764 m way. EXTENDED by graph walk: +0 segment(s) at base, +1 at top (stop: base=no_descending_continuation, top=no_ascending_continuation; min_avg=2.0%). Review before adopting. DEDUPE: absorbed 1 overlapping proposal(s): discovered-lane-51-8508-3-2336 ADOPTED (notable slice 2026-08-11): big-gain. AUTO-NAMED from gazetteer (hypothesis, unreviewed): was 'Discovered lane (51.8486, -3.2344)'.",
"naming_note": "auto-named from gazetteer (hypothesis, unreviewed); discovered as 'Discovered lane (51.8486, -3.2344)'"
}