Ground movement

What we use

European Ground Motion Service (EGMS), the European service that measures ground movement with the Sentinel-1 satellites. It is part of the European Union's Copernicus programme and is run by the European Environment Agency. We use the Ortho product, vertical movement only: measurement points on a 100 metre grid, each with the speed at which the ground is sinking or rising, in millimetres a year, and its movement month by month. The period measured is 2020-2024, in the edition published on 29 April 2026. Copernicus data is free and open to use, with credit to the source.

How we use it

The report takes the measurement points within 50 metres of the cadastral plot (the cadastral parcel), or of the address point when there is no plot. If there are at least 3 it uses those, otherwise it widens the search to 250 metres. It works out the median of their speeds, the middle value, and reads it like this:

• stable ground: between 2 mm a year down and 2 mm a year up, within the typical uncertainty of the measurement;
• slow sinking: more than 2 mm and less than 5 mm a year downwards;
• noticeable sinking: 5 mm a year or more downwards;
• rising: more than 2 mm a year upwards.

Stable ground is favourable, slow sinking and rising are worth considering, noticeable sinking is critical: the meaning of the levels is in the methodology. The section also shows how many points it used, the slowest and the fastest, the distance of the nearest point and a table of the points within 50 and 250 metres. If the speed varies by 4 mm a year or more among nearby points, it says so: different movements over a short distance can put more strain on structures than even sinking.

The chart of recent years

The chart shows how many millimetres the ground has moved month by month, relative to the first measurement: it is the median of the 5 nearest points within 250 metres. Below zero the ground has sunk. The report does not show the individual measurement points: only counts, speeds and this trend.

Limits

• The points describe the trend in the area, not the condition of the individual building: cracks and settling can only be established by an inspection from a qualified professional.
• The measurements are accurate to 1-2 mm a year: that is why below 2 mm the report treats the ground as stable.
• The points sit on a 100 metre grid and do not follow a specific building.
• Where there are no stable surfaces to reflect the signal, such as fields, woods or areas with dense vegetation, there are no points. The section says so, and it does not mean the ground is still.
• Only vertical movement counts, over the period 2020-2024: anything that happened before or after does not appear.
• Landslides are a separate topic, with their own maps: Landslides and floods.

Official page: EGMS Ortho from Copernicus.