Wenallt to Cwm Grognant°
1088.2 m · net rise 85.8 m · total ascent 97.9 m · overall 7.9% · confidence: good · Cwm Grognant · Ceredigion
Shape: sustained — 42% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 86 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 (52.3225, -3.9555)'). Corrections welcome.
≈ Overhead cover (tree canopy or structures) spans 48% 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) | ≈53% | 1029–1031 m | under overhead cover terrain reads 123.8% at 608–610 m across a structure — excluded |
| 3 m (diagnostic) | ≈49% | 1028–1031 m | under overhead cover terrain reads 114.6% at 608–611 m across a structure — excluded |
| 5 m | ≈36% | 1029–1034 m | under overhead cover terrain reads 93.5% at 606–611 m across a structure — excluded |
| 10 m | ≈29% | 561–571 m | under overhead cover terrain reads 54.9% at 604–614 m across a structure — excluded |
| 20 m | ≈22.9% | 551–571 m | under overhead cover terrain reads 29.1% at 563–583 m across a structure — excluded |
| 25 m | ≈20.1% | 546–571 m | under overhead cover terrain reads 28.5% at 558–583 m across a structure — excluded |
| 50 m | ≈18.0% | 521–571 m | under overhead cover terrain reads 21.1% at 545–595 m across a structure — excluded |
| 100 m | ≈17.1% | 471–571 m | under overhead cover terrain reads 19.0% at 495–595 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
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_22_266270_20220114dtm.tif",
"data/cache/wales/dtm_1m/wg_del_22_266271_20220114dtm.tif",
"data/cache/wales/dtm_1m/wg_del_22_267270_20220114dtm.tif",
"data/cache/wales/dtm_1m/wg_del_22_267271_20220114dtm.tif"
],
"calculated_at": "2026-08-12T09:08:17+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_22_266270_20220114dtm.tif",
"wg_del_22_266271_20220114dtm.tif",
"wg_del_22_267270_20220114dtm.tif",
"wg_del_22_267271_20220114dtm.tif"
],
"elevation_capture_dates": [
"14-01-2022"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 10.2% over 200 m (Terrain 50), gain 44.6 m over 485 m way. EXTENDED by graph walk: +2 segment(s) at base, +0 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-52-3253-3-9531 ADOPTED (notable slice 2026-08-11): qualified-steep. AUTO-NAMED from gazetteer (hypothesis, unreviewed): was 'Discovered lane (52.3225, -3.9555)'.",
"naming_note": "auto-named from gazetteer (hypothesis, unreviewed); discovered as 'Discovered lane (52.3225, -3.9555)'"
}