Horner's Green to Castling's Heath
320.0 m · net rise 17.6 m · total ascent 22.4 m · overall 5.5% · evidence quality B (good) · Groton · Suffolk · share
Shape: stepped — 56% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 58 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.
≈ Overhead cover (tree canopy or structures) spans 20% 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) | ≈31% | 136–138 m | under overhead cover terrain reads 47.3% at 270–272 m across a structure — excluded |
| 3 m (diagnostic) | ≈27% | 228–231 m | under overhead cover terrain reads 43.3% at 269–272 m across a structure — excluded |
| 5 m | ≈22% | 226–231 m | under overhead cover terrain reads 39.2% at 268–273 m across a structure — excluded |
| 10 m | ≈17% | 221–231 m | under overhead cover terrain reads 32.2% at 266–276 m across a structure — excluded |
| 20 m | ≈16.3% | 211–231 m | under overhead cover terrain reads 24.9% at 263–283 m across a structure — excluded |
| 25 m | ≈15.6% | 206–231 m | under overhead cover terrain reads 21.0% at 263–288 m across a structure — excluded |
| 50 m | ≈13.6% | 200–250 m | under overhead cover terrain reads 15.7% at 234–284 m across a structure — excluded |
| 100 m | ≈11.2% | 160–260 m | under overhead cover terrain reads 14.5% at 182–282 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
No aerial layer here: Britain has no open or government source of aerial photography at road scale — the pan-government APGB imagery is licensed to the public sector only, unlike the LiDAR this survey is measured from. Street View, where it exists, is the visual check.
This climb's data: OCL JSON — the full gradient ladder, quality flags and provenance in the OpenClimb Ladder format.
Access: Listed 2026-09-15 (line off the mapped road — the 2026-09-11 rule): the steepest 25 m sits well off the road authority's centreline (6.2 m) and the coarse national terrain model disagrees with the LiDAR there by (10.0 pp) — together a sign the measured line has left the road onto steeper ground. Held from the rankings until re-lined to the centreline and re-measured. Peter 2026-09-15: the steepest 25 m sits off the mapped road while the rest of the line is on it — kept listed, not retired.
Measured, not vetted. This page records what the laser record shows about the road's shape — nothing more. Nobody has necessarily ridden or inspected this road for the survey, and a page here is not a recommendation and no guarantee that the road is open, surfaced, rideable or safe. Gates, private sections, missing rights of way and hazards do not show up in elevation data. Check access and conditions on the ground and make your own judgment.
Ridden it, or know better? Submit data for this climb no account needed · Share this climb
Route colour = gradient over a 25 m window: <10% 10–20% 20–25% ≥25%
© OpenStreetMap contributors · topo tiles © OpenTopoMap (CC-BY-SA) · vector tiles OpenFreeMap
Profile
The map, profile and gradient chart share one position — move your pointer over them and the marker follows. Colors are the gradient bands; the shaded span is the steepest 25 m. Any 25 m figure is good to about a point either way (why).
Measurement card
| Elevation | Environment Agency — EA LIDAR Composite DTM 1m (2022) |
|---|---|
| Resolution / CRS | 1.0 m grid, EPSG:27700; sampled every 1.0 m, bilinear interpolation |
| Tiles | E596000_N240000_2000m.tif, E596000_N242000_2000m.tif |
| Road centreline | OpenStreetMap (local PBF extract), snapshot 2026-08-26T20:22:15Z |
| Quality status | evidence quality B; caveated windows: canopy or structure, texture excluded |
| Analysis | OCL 0.1.0, analysis 0.1.0, run retro-260914, calculated 2026-09-15 |
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/england/dtm_1m/E596000_N240000_2000m.tif",
"data/cache/england/dtm_1m/E596000_N242000_2000m.tif"
],
"calculated_at": "2026-09-15T02:33:36+00:00",
"road_source": "OpenStreetMap (local PBF extract)",
"road_attribution": "\u00a9 OpenStreetMap contributors, ODbL",
"osm_pbf_path": "data/cache/pbf/england-2026-08-27.osm.pbf",
"osm_snapshot": "2026-08-26T20:22:15Z",
"run_id": "retro-260914",
"elevation_provider": "Environment Agency",
"elevation_dataset": "EA LIDAR Composite DTM 1m (2022)",
"elevation_licence": "Open Government Licence v3 \u2014 \u00a9 Environment Agency",
"elevation_coverage_id": "13787b9a-26a4-4775-8523-806d13af58fc__Lidar_Composite_Elevation_DTM_1m",
"elevation_tile_ids": [
"E596000_N240000_2000m.tif",
"E596000_N242000_2000m.tif"
],
"route_cut_m": 320.0,
"climb_origin": "discovered",
"structure_own_ways": "none \u2014 the route carried no way list; own decks unmasked",
"license": "ODbL-1.0",
"license_url": "https://howsteep.org/licensing"
}