Trallong to Cwm Brynych°
4832.8 m · gain 159.9 m · overall 3.3% · Cwm Camlais-fach · Powys
Shape: sustained — 38% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 103 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 (51.9247, -3.5260)'). Corrections welcome.
≈ Overhead cover (tree canopy or structures) spans 17% 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) | ≈53.2% | 2173–2175 m | under overhead cover terrain reads 53.9% at 3509–3511 m across a structure — excluded |
| 3 m (diagnostic) | 45.3% | 2172–2175 m | |
| 5 m | 37.7% | 2173–2178 m | |
| 10 m | 33.2% | 2172–2182 m | |
| 20 m | 27.0% | 2172–2192 m | |
| 25 m | 24.7% | 2172–2197 m | |
| 50 m | ≈18.3% | 2172–2222 m | under overhead cover terrain reads 19.4% at 3461–3511 m across a structure — excluded |
| 100 m | ≈12.9% | 2172–2272 m | under overhead cover terrain reads 17.8% at 3466–3566 m across a structure — excluded |
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_294225_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_294226_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_294227_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_294228_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_295225_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_295226_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_295227_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_295228_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_296225_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_296226_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_296227_20211201dtm.tif",
"data/cache/wales/dtm_1m/wg_del_18_296228_20211201dtm.tif"
],
"calculated_at": "2026-08-12T09:07:30+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_294225_20211201dtm.tif",
"wg_del_18_294226_20211201dtm.tif",
"wg_del_18_294227_20211201dtm.tif",
"wg_del_18_294228_20211201dtm.tif",
"wg_del_18_295225_20211201dtm.tif",
"wg_del_18_295226_20211201dtm.tif",
"wg_del_18_295227_20211201dtm.tif",
"wg_del_18_295228_20211201dtm.tif",
"wg_del_18_296225_20211201dtm.tif",
"wg_del_18_296226_20211201dtm.tif",
"wg_del_18_296227_20211201dtm.tif",
"wg_del_18_296228_20211201dtm.tif"
],
"elevation_capture_dates": [
"01-12-2021"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 12.6% over 200 m (Terrain 50), gain 92.2 m over 2701 m way. EXTENDED by graph walk: +3 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): clean-steep. AUTO-NAMED from gazetteer (hypothesis, unreviewed): was 'Discovered lane (51.9247, -3.5260)'.",
"naming_note": "auto-named from gazetteer (hypothesis, unreviewed); discovered as 'Discovered lane (51.9247, -3.5260)'"
}