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Llanarth to Synod Inn / Post Mawr^°

3396.1 m · gain 110.3 m · overall 3.2% · Pen-cae · Sir Ceredigion - Ceredigion

Shape: stepped — 48% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 169 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 (52.1809, -4.3172)'). Corrections welcome.

≈ Overhead cover (tree canopy or structures) spans 6% 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?

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.

Topo (contours) Vector   © 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_24_240254_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_240255_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_240256_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_240257_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_241254_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_241255_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_241256_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_241257_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_242254_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_242255_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_242256_20220120dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_24_242257_20220120dtm.tif"
  ],
  "calculated_at": "2026-08-12T23:12:10+00:00",
  "road_source": "trunk-adopted-routes/discovered-lane-52-1809-4-3172.geojson",
  "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_24_240254_20220120dtm.tif",
    "wg_del_24_240255_20220120dtm.tif",
    "wg_del_24_240256_20220120dtm.tif",
    "wg_del_24_240257_20220120dtm.tif",
    "wg_del_24_241254_20220120dtm.tif",
    "wg_del_24_241255_20220120dtm.tif",
    "wg_del_24_241256_20220120dtm.tif",
    "wg_del_24_241257_20220120dtm.tif",
    "wg_del_24_242254_20220120dtm.tif",
    "wg_del_24_242255_20220120dtm.tif",
    "wg_del_24_242256_20220120dtm.tif",
    "wg_del_24_242257_20220120dtm.tif"
  ],
  "elevation_capture_dates": [
    "20-01-2022"
  ],
  "climb_origin": "discovered",
  "notes": "Coarse pass: max 10.8% over 200 m (Terrain 50), gain 82.3 m over 2869 m way. EXTENDED by graph walk: +2 segment(s) at base, +4 at top (stop: base=no_descending_continuation, top=no_ascending_continuation; min_avg=2.0%). Review before adopting. ADOPTED (trunk sweep, Peter's on-sight verdict 2026-08-12): clean table, adopt-all. AUTO-NAMED from gazetteer (hypothesis, unreviewed): was 'Discovered lane (52.1809, -4.3172)'.",
  "naming_note": "auto-named from gazetteer (hypothesis, unreviewed); discovered as 'Discovered lane (52.1809, -4.3172)'"
}