A boundary is a line between surveyed points, and with a survey grade receiver a point is fixed to a centimetre against a national reference that does not drift. One hedge on one farm is thirty centimetres east of where it was fixed in 2017, and the hedge has not been touched.
I am a land surveyor and most of my rural work is boundaries.
How a boundary is fixed.
You occupy points along it with a survey grade satellite receiver, which gets a fix to about a centimetre against a national reference network of fixed stations, and you record the coordinates. You put a nail or a pin in at the ends so the points can be reoccupied. The hedge, the fence and the ditch are then described relative to those points, and the whole thing goes on a plan for the deeds.
Ten years later somebody can find the pin, occupy it, and get the same coordinates to a centimetre or two. That is the promise of the trade.
On one farm there is a hedge line about a hundred and forty metres long that I fixed in 2017 for a sale.
I have reoccupied its points every year since, because the farmer asked me to after the first time it happened.
The hedge is about two metres east of where it was in 2017. Thirty centimetres a year, near enough, in a straight line.
The pins have not moved. I want to say that first. The pins at each end, in the ground, occupy to the 2017 coordinates within two centimetres every year.
The hedge, the ditch beside it, and the fence in it have moved east relative to the pins.
What has been checked.
The receiver. Different receivers on different years, on the same pins, agreeing with each other and with 2017.
The reference network. It is what the country's mapping is fixed to and it is monitored continuously for exactly this, and it has not moved.
The ground. This is where a surveyor expects to find the answer, because ground does move: landslip, subsidence, shrinkable clay. So I put in four more pins across the field in 2019, in a line at right angles to the hedge, and I reoccupy them too.
None of them has moved. The field is stable to two centimetres across its whole width.
The hedge, standing in stable ground, between stable pins, has moved two metres.
What a hedge moving two metres looks like, because I have thought about this a great deal.
A hedge is roots in the ground, and the roots have not been dug up and moved, and there is no fresh soil and no line of old root holes to the west of it. The ditch beside it is a ditch with old spoil and old vegetation on its banks, and it is where the hedge is, and there is no filled ditch to the west.
The fence in the hedge has posts, and the posts are old and grey and weathered on the same faces they were weathered on in 2017, and in 2017 they were two metres west of where they are.
Everything about that boundary is where a boundary would be if it had been there for a hundred years, and my coordinates say it was two metres away seven years ago, and my coordinates are right.
What is done about it.
The plan on the deeds shows the 2017 line, and the boundary on the ground is now inside the neighbour's field by two metres, and neither farmer has raised it, because the neighbour has not noticed and my client would rather not have the conversation.
I have written it up for my professional body as an anomaly with the raw observations attached. The response, which was courteous, was that the observations were internally consistent and that they would be interested in a further year of data.
They have had six.
What I do.
I reoccupy the pins in the spring and I add a year to the plot.
The one change is that I do not stand in the hedge line to measure it.
To fix the hedge you occupy points along its centre line, in the hedge, on a pole. That is how it is done and it takes a morning.
I fix it from the field now, with a total station from a pin, which is slower and just as good.
The reason is a morning in 2021 when I was standing in the hedge with the pole, waiting for the receiver to settle, and the fix came in, and the coordinates on the screen were walking. Not scatter. Walking east, at about a millimetre a second, while I stood still with the pole plumb on a point I could feel under my boot, and I watched it walk for a minute, and then I stepped out into the field and the number stopped.