What a result can and can't tell you
Satellite radar is remarkably precise, but it measures something specific. Here is exactly what that is, and what it isn't.
What it tells you
- How the ground and buildings in a 100 m square moved up or down between January 2020 and December 2024, relative to the ground 1–3 km around it.
- Whether that movement is steady, speeding up or slowing down, and whether it follows a yearly swelling-and-shrinking cycle typical of clay soils.
- How your square compares with every other measured square within 3 km.
What it can't tell you
- It is not a survey. It can’t see cracks, drains, trees, foundations or the condition of a building.
- It is an average of a 100 m square, centred on your postcode’s centre point. One home in that square can behave differently from its neighbours.
- It covers 2020–2024. Movement can change, for example after an unusually dry summer or building work nearby.
- It measures vertical movement. Sideways movement, such as on some slopes, is not shown in this release.
- It needs stable radar echoes. Fields, woodland, water and some rural areas often have no measurement. When that happens we say so rather than guess.
How precise it is
Each result shows a 95% range, typically about ±1 mm a year. That range includes both the measurement noise in your square and an allowance for errors shared across the whole dataset. In tests on data where the true answer is known, our ranges contain the right value 92–95% of the time.
To put a millimetre a year in context: many UK homes show seasonal clay movement of several millimetres between summer and winter, and most structures tolerate small, even movements without damage. The pattern and the rate matter more than any single number.
Very large or unusual results
Movements faster than 10 mm a year are rare under UK homes. They can be real, for example over old mine workings or made ground, but they can occasionally come from processing artefacts. Those results always carry a note recommending independent confirmation. In former coalfields, the Mining Remediation Authority can advise.
Independent review
Our method is published in full on the method page. We are arranging an independent review of the method by a specialist in satellite radar. We’ll publish the reviewer’s findings here once it is complete.
How to use a result
- Steady: reassuring, alongside a normal survey.
- Slow movement: worth mentioning to your surveyor, especially with clay soils or large trees nearby.
- Worth checking: ask a surveyor or structural engineer to look before relying on the property’s condition.