Aerial survey of land and sites around Ivybridge

The moor drops steeply to the South Hams here and the Erme runs out of it through a valley that funnels and gusts. A forecast figure taken for the district is close to useless on that ground: what matters is what the air is doing at survey height above a particular slope on a particular afternoon.

The tell is gusting rather than steady wind. A steady breeze at the top of the aircraft's range is workable; the same average made up of lulls and hard gusts is not, because the aircraft is fighting to hold station and the frames stop overlapping the way the plan assumed. On this ground that judgement is made on site.

The boundary between the enclosed fields and the open moor is the feature most often wanted here, and it is a genuine one on the ground: a wall, a bank, a change in vegetation, sometimes all three and sometimes none of them.

From above that line reads clearly, which is exactly why people ask for it. What the survey provides is a dated, measurable picture of where the physical boundary sits. Where it corresponds to a legal boundary is a question for somebody qualified to answer it, and this survey does not pretend to.

The northern side of the town sits noticeably higher than the southern side, and holdings that run up towards the moor gain a lot of height quickly. A plan flown level over that gets progressively closer to the ground as it climbs.

Splitting the parcel by height band solves it and costs a little more flying time. On the steepest ground it is also the safe answer rather than merely the tidy one, which is why it is decided at planning rather than adjusted in the field.

Rainfall on the moor edge is high and the wet spells are long. Between November and February a usable day can be a few hours rather than a whole one, and the flight has to fit inside the window rather than the window accommodating the flight.

Larger holdings here are therefore often planned as two visits from the outset. That is said in the quote, not discovered halfway through the first afternoon when the light goes.

This is largely a late twentieth century town, and the ground that gets surveyed around it is often the space between the estates: drainage corridors, wooded strips, verges, attenuation ponds, land held by nobody in particular until a question arises about it.

Those parcels are small, awkward and well suited to aerial capture, because walking them proves very little and one flight shows how they actually connect, where water goes and what condition the access is in.

The main line and its structures run across this valley, and infrastructure of that kind is corridor work: flown as a strip along the alignment with overlap down its length and enough width to carry the embankments, cuttings and drainage either side.

Anything near an operating railway needs the operator's agreement and a plan that keeps the aircraft clear, which is a conversation to have before a date is offered. Vegetation on cuttings and embankments is one of the most common reasons this sort of capture is asked for, and it is a subject that reads far better from above than from a lineside walk.