Welsh Harp Hollow
3695.0 m · gain 303.6 m · overall 8.2% · Cwm y Sul · Powys
Shape: sustained — 41% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 199 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.
≈ Overhead cover (tree canopy or structures) spans 26% 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) | ≈41.9% | 2671–2673 m | under overhead cover |
| 3 m (diagnostic) | ≈37.0% | 2670–2673 m | under overhead cover |
| 5 m | 33.2% | 2128–2133 m | |
| 10 m | ≈29.4% | 2124–2134 m | under overhead cover |
| 20 m | 24.5% | 2637–2657 m | |
| 25 m | 23.1% | 2632–2657 m | |
| 50 m | ≈20.6% | 844–894 m | under overhead cover |
| 100 m | ≈18.8% | 829–929 m | under overhead cover |
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_13_325307_20210316dtm.tif",
"data/cache/wales/dtm_1m/wg_del_13_325308_20210316dtm.tif",
"data/cache/wales/dtm_1m/wg_del_13_326307_20210316dtm.tif",
"data/cache/wales/dtm_1m/wg_del_13_326308_20210316dtm.tif",
"data/cache/wales/dtm_1m/wg_del_13_327307_20210316dtm.tif",
"data/cache/wales/dtm_1m/wg_del_13_327308_20210316dtm.tif"
],
"calculated_at": "2026-08-12T09:11:29+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_13_325307_20210316dtm.tif",
"wg_del_13_325308_20210316dtm.tif",
"wg_del_13_326307_20210316dtm.tif",
"wg_del_13_326308_20210316dtm.tif",
"wg_del_13_327307_20210316dtm.tif",
"wg_del_13_327308_20210316dtm.tif"
],
"elevation_capture_dates": [
"16-03-2021"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 17.6% over 200 m (Terrain 50), gain 273.3 m over 2869 m way. EXTENDED by graph walk: +0 segment(s) at base, +3 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."
}