Cefn Llan
218.5 m · gain 42.4 m · overall 19.4% · Cwmpadarn · Sir Ceredigion - Ceredigion
Shape: sustained — 34% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 219 m.
Documented on the ground — sign: 32% (2025). Signs get repainted and tags get retagged, so the date is part of the fact; on no cycling list we know of.
≈ Overhead cover (tree canopy or structures) spans 46% 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) | ≈32.1% | 61–63 m | under overhead cover |
| 3 m (diagnostic) | ≈30.9% | 59–62 m | under overhead cover |
| 5 m | ≈29.1% | 58–63 m | under overhead cover |
| 10 m | ≈28.4% | 52–62 m | under overhead cover |
| 20 m | ≈27.5% | 42–62 m | under overhead cover |
| 25 m | ≈27.4% | 41–66 m | under overhead cover |
| 50 m | ≈26.6% | 20–70 m | under overhead cover |
| 100 m | ≈25.1% | 1–101 m | under overhead cover |
may_start_earliermay_continue_beyond_end 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 · OSM way 218612917 highlights the mapped road · geojson.io our exact measured line · OpenTopoMap
© OpenStreetMap contributors · topo tiles © OpenTopoMap (CC-BY-SA) · vector tiles OpenFreeMap
Profile
Reported values vs. measurement
| Source | Claim | Evidence | Best-matching window |
|---|---|---|---|
| Road sign (current) | 32% | road_sign | 2 m (-0.1 pp) |
| Road sign (historic, pre-2025) | 25% | road_sign | 100 m (-0.1 pp) |
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_23_260281_20220117dtm.tif",
"data/cache/wales/dtm_1m/wg_del_29_259281_20220319dtm.tif"
],
"calculated_at": "2026-08-12T09:11:46+00:00",
"road_source": "OpenStreetMap (local PBF extract)",
"road_attribution": "\u00a9 OpenStreetMap contributors, ODbL",
"osm_ids": [
218612917,
103333437
],
"osm_versions": {
"218612917": 7,
"103333437": 8
},
"osm_timestamps": {
"218612917": "2025-11-05 02:22:20+00:00",
"103333437": "2026-03-11 04:39:45+00:00"
},
"osm_retrieved_at": "2026-08-12T09:11:45+00:00",
"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_23_260281_20220117dtm.tif",
"wg_del_29_259281_20220319dtm.tif"
],
"elevation_capture_dates": [
"17-01-2022",
"19-03-2022"
],
"route_cut_m": 218.5,
"climb_origin": "named",
"signed_gradient_pct": 32,
"signed_source": "Road sign at foot of hill. OSM tag history dates the change: incline=-25% from 2013 (user Pobice), updated to -32% on 2025-10-22 (changeset 173626481, user Fgjgdrou). Two independent mappers 12 years apart = strong sign evidence.",
"notes": "Golden regression case. Aberystwyth. Sibling segment 218612916 still carries the stale -25% \u2014 both sign eras preserved in OSM."
}