# BT Tower · London — sources and limits
Prepared 14 October 2026. Concrete telecom landmark; cylindrical shaft, former aerial galleries and upper public floors.
Structure account: https://en.wikipedia.org/wiki/BT_Tower
Institutional / site evidence: https://newsroom.bt.com/bt-group-announces-sale-of-bt-tower-to-mcr-hotels/
Nominal origin [latitude, longitude]: [51.5215, -0.1389]. Public mapped position, not surveyed mast base.

## Model
Nominal envelope 189 m. Shapes, widths, guys, wire circuits, platforms and dishes are reconstructed. No internal or operational configuration is represented. FM/DAB centres follow the archived Ofcom workbook where available. On multi-mast sites, OSM positions are used when available; untagged heights and connecting wires remain schematic. LOS reference is the nominal origin, not a certified attachment point. Alexandra Palace total height is an explicit approximation. BT London represents its landmark exterior, not a confirmed operational inventory or completed hotel conversion.

## Terrain and context
Local OSM context covers a 1 km square centred on the site, marked by a cyan boundary. The remaining 6 km landscape has regional terrain only. Uncollected buildings and trees are unknown, not absent.
Regional Tilezen Terrarium tiles, source URLs, provider headers and SHA256 retained in research/thirty/bt-london/terrain-sources.json. 6 km radius, 12.3 km square envelope, 25 m resampled grid. Output resolution is not native survey accuracy. The neutral grey map outside collected landcover is terrain shading, not aerial photography. Coastline geometry is not extrapolated from a partial map; no precise sea/tidal boundary is claimed.
Buildings: OSM height tags, levels × 3 m or assumed 7 m; maximum visual height 100 m. Simplified footprint extrusions omit courtyards. Woodland uses assumed 10 m clusters. Surface and vegetation analysis grids remain entirely unknown. Visual geometry is excluded from LOS; no RF, curvature, refraction or Fresnel model.

## Interest evidence
112,073 annual article views, rank 1 among screened eligible candidates. 1 October 2025–30 September 2026. Not search volume, unique visitors or UK-only users. Full screening decisions and monthly data: ../interest.json.

## Services
Ofcom FM, DAB, MF and TV main-plan workbook rows retrieved 3 October 2026. These are dated records, not proof of live carriage. MF uses EMRP, FM/DAB use ERP. Complete tenants, shortwave schedules, satellite services, mobile networks, local TV and relay inventories are unresolved.

## Attribution
© OpenStreetMap contributors, ODbL: https://www.openstreetmap.org/copyright
Terrain: https://registry.opendata.aws/terrain-tiles/ ; source credits https://github.com/tilezen/joerd/blob/master/docs/attribution.md
Ofcom: OGL v3.0. Wikimedia pageview analytics: CC0. Three.js: MIT, see THREE-LICENSE.txt. Article prose is paraphrased; no reference photos redistributed.