Evidence pack · England
ZTV / Visibility Report
Bare-earth and screened zones of theoretical visibility to 2 km, computed from surveyed ground with a methods note stating every parameter used.
£129
One-off. Delivered by email within the hour, or refunded automatically if it cannot be produced.
See a real sample — Chiltern scarp (PDF)
Two figures, and the gap between them is the point
A zone of theoretical visibility maps where a site has a geometrically clear line of sight to it. You get two, always reported apart:
- Bare earth. Landform only — where the topography alone fails to hide the site. The conservative maximum, and the one a landscape officer expects to see first.
- Screened. The same calculation with the surveyed surface model, so woodland, hedgerows and buildings block the view as they stood when the survey was flown.
Their difference is your screening story. On the sample — a wooded chalk scarp — the bare-earth zone covers 26.6% of the study area and the screened one 7.3%: existing vegetation is doing nearly three quarters of the work, and vegetation can be felled. Blending the two into a single map would delete exactly that.
Built to be checked
- A methods note that states every parameter. Observer height (1.6 m), target height, study radius, both surfaces, both survey years, the lattice, and the curvature correction — generated from the values actually used, so it cannot drift from the computation it describes. Two ZTVs of the same site can differ by a factor of three on observer height alone; without its parameters a ZTV is a picture, not evidence.
- Earth curvature and refraction, applied throughout.The standard survey correction, which is 0.27 m at 2 km. Omitting it silently over-states visibility against distant ridge lines.
- Observers around the boundary, not one pin. A long frontage is visible from places its centre is not.
- A viewpoint table. Sampled positions on sixteen bearings at three distances, each with both answers.
What it is not
Theoretical is the load-bearing word. This maps where the line of sight is geometrically clear in the model. It does not say the site will be noticed, or seen in typical weather, or looked at by anyone facing that way — and it makes no judgement about whether any of it matters, which is the assessment itself.
- These are sampled positions, not assessment viewpoints. GLVIA3 viewpoints are chosen by a landscape architect for who uses them and what they represent. A ring of compass bearings is a starting point for that choice, not a substitute for it.
- The study surface is 10 m, and that is deliberate.A landscape ZTV at 1 m would be false precision — GLVIA3 practice is 5–50 m — and the answer would not improve.
- The surface model is a snapshot. Anything built, demolished, grown or felled since the survey is not represented, and the survey year is stamped on both figures.
- It needs a site boundary. A ZTV is computed from the edges of a site, so draw the red line or let us snap a pin to its registered parcel.
Coverage
England only, to a 2 km study radius. Both surfaces are the Environment Agency’s national LiDAR composite; where it has never been flown there is no visibility to compute and the order refunds.
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