Groeslon-waun to Cefn Du°
1714.4 m · gain 98.3 m · overall 5.7% · Groeslon · Gwynedd
Shape: stepped — 51% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 106 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 (53.1173, -4.1790)'). Corrections welcome.
Gradient ladder what do windows mean?
| Window | Maximum | Located at | |
|---|---|---|---|
| 2 m (diagnostic) | 28.3% | 33–35 m | |
| 3 m (diagnostic) | 27.9% | 32–35 m | |
| 5 m | 27.9% | 30–35 m | |
| 10 m | 26.9% | 25–35 m | |
| 20 m | 26.6% | 16–36 m | |
| 25 m | 26.2% | 14–39 m | |
| 50 m | 24.1% | 4–54 m | |
| 100 m | 18.2% | 0–100 m |
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_11_253359_20210302dtm.tif",
"data/cache/wales/dtm_1m/wg_del_11_253360_20210302dtm.tif",
"data/cache/wales/dtm_1m/wg_del_11_254359_20210302dtm.tif",
"data/cache/wales/dtm_1m/wg_del_11_254360_20210302dtm.tif",
"data/cache/wales/dtm_1m/wg_del_11_255359_20210302dtm.tif",
"data/cache/wales/dtm_1m/wg_del_11_255360_20210302dtm.tif"
],
"calculated_at": "2026-08-12T09:09:50+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_11_253359_20210302dtm.tif",
"wg_del_11_253360_20210302dtm.tif",
"wg_del_11_254359_20210302dtm.tif",
"wg_del_11_254360_20210302dtm.tif",
"wg_del_11_255359_20210302dtm.tif",
"wg_del_11_255360_20210302dtm.tif"
],
"elevation_capture_dates": [
"02-03-2021"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 11.4% over 200 m (Terrain 50), gain 75.3 m over 1581 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. ROAD-REVIEW: way 333171342: unnamed service way; way 333171342: service way, surface untagged ADOPTED (notable slice 2026-08-11): clean-steep,qualified-steep. AUTO-NAMED from gazetteer (hypothesis, unreviewed): was 'Discovered lane (53.1173, -4.1790)'.",
"naming_note": "auto-named from gazetteer (hypothesis, unreviewed); discovered as 'Discovered lane (53.1173, -4.1790)'"
}