Tal-y-bont to Pen-y-gaer°
3380.8 m · gain 335.3 m · overall 9.9% · Llanbedr-y-cennin · Conwy
Shape: sustained — 30% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 212 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 (53.2120, -3.8669)'). Corrections welcome.
needs review short_window_divergence — treat short-window maxima here as provisional.
≈ Overhead cover (tree canopy or structures) spans 40% 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) | ≈48.9% | 1105–1107 m | under overhead cover |
| 3 m (diagnostic) | ≈45.1% | 1105–1108 m | under overhead cover |
| 5 m | ≈38.9% | 1105–1110 m | under overhead cover terrain reads 42.6% at 997–1002 m across a structure — excluded |
| 10 m | ≈27.2% | 1102–1112 m | under overhead cover terrain reads 33.5% at 995–1005 m across a structure — excluded |
| 20 m | ≈23.6% | 3129–3149 m | under overhead cover terrain reads 24.9% at 985–1005 m across a structure — excluded |
| 25 m | 23.6% | 3125–3150 m | |
| 50 m | ≈21.2% | 3115–3165 m | under overhead cover terrain reads 21.9% at 954–1004 m across a structure — excluded |
| 100 m | ≈19.1% | 2727–2827 m | under overhead cover terrain reads 19.4% at 907–1007 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_12_274368_20210302dtm.tif",
"data/cache/wales/dtm_1m/wg_del_12_274369_20210307dtm.tif",
"data/cache/wales/dtm_1m/wg_del_12_274370_20210307dtm.tif",
"data/cache/wales/dtm_1m/wg_del_12_275368_20210302dtm.tif",
"data/cache/wales/dtm_1m/wg_del_12_275369_20210307dtm.tif",
"data/cache/wales/dtm_1m/wg_del_12_275370_20210307dtm.tif",
"data/cache/wales/dtm_1m/wg_del_12_276368_20210302dtm.tif",
"data/cache/wales/dtm_1m/wg_del_12_276369_20210307dtm.tif",
"data/cache/wales/dtm_1m/wg_del_12_276370_20210307dtm.tif"
],
"calculated_at": "2026-08-12T09:10:12+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_12_274368_20210302dtm.tif",
"wg_del_12_274369_20210307dtm.tif",
"wg_del_12_274370_20210307dtm.tif",
"wg_del_12_275368_20210302dtm.tif",
"wg_del_12_275369_20210307dtm.tif",
"wg_del_12_275370_20210307dtm.tif",
"wg_del_12_276368_20210302dtm.tif",
"wg_del_12_276369_20210307dtm.tif",
"wg_del_12_276370_20210307dtm.tif"
],
"elevation_capture_dates": [
"07-03-2021"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 15.1% over 200 m (Terrain 50), gain 167.8 m over 1509 m way. EXTENDED by graph walk: +4 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 4 overlapping proposal(s): discovered-lane-53-2056-3-8511, discovered-lane-53-2075-3-8589, discovered-lane-53-2078-3-8790, discovered-lane-53-2086-3-8625 ADOPTED (notable slice 2026-08-11): big-gain. AUTO-NAMED from gazetteer (hypothesis, unreviewed): was 'Discovered lane (53.2120, -3.8669)'.",
"naming_note": "auto-named from gazetteer (hypothesis, unreviewed); discovered as 'Discovered lane (53.2120, -3.8669)'"
}