Sennybridge to Yr Allt°
1412.2 m · gain 55.5 m · overall 3.9% · Cwm Clydach · Powys
Shape: sustained — 38% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 70 m.
An unlisted find of this survey, on no list we know of. It was discovered by analysing LiDAR terrain data and cross-checked against the OS road network, surface models and map tags — but despite all that, 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 that someone is you, 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 appears on no list we know of, 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 (51.9430, -3.5793)'). Corrections welcome.
≈ Overhead cover (tree canopy or structures) spans 39% 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) | 49.9% | 120–122 m | |
| 3 m (diagnostic) | 48.0% | 120–123 m | |
| 5 m | ≈43.9% | 119–124 m | under overhead cover terrain reads 45.3% at 738–743 m across a structure — excluded |
| 10 m | 39.7% | 120–130 m | |
| 20 m | ≈32.1% | 116–136 m | under overhead cover |
| 25 m | ≈29.5% | 110–135 m | under overhead cover |
| 50 m | ≈21.9% | 105–155 m | under overhead cover terrain reads 22.2% at 40–90 m across terrain that holds no road surface (dense canopy, no bench) — excluded |
| 100 m | ≈15.1% | 103–203 m | under overhead cover terrain reads 19.7% at 45–145 m across terrain that holds no road surface (dense canopy, no bench) — excluded |
may_start_earlier 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
© 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_18_290228_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_291228_20211201dtm.tif"
],
"calculated_at": "2026-08-12T09:07:33+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_18_290228_20211201dtm.tif",
"wg_del_18_291228_20211201dtm.tif"
],
"elevation_capture_dates": [
"01-12-2021"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 14.3% over 200 m (Terrain 50), gain 29.0 m over 204 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. ADOPTED (notable slice 2026-08-11): qualified-steep. AUTO-NAMED from gazetteer (hypothesis, unreviewed): was 'Discovered lane (51.9430, -3.5793)'.",
"naming_note": "auto-named from gazetteer (hypothesis, unreviewed); discovered as 'Discovered lane (51.9430, -3.5793)'"
}