Ground-stability products can help identify a question about a site, but they describe different kinds of susceptibility. The British Geological Survey’s GeoSure maps geological conditions across Great Britain. Its separate Property Subsidence Assessment (PSA) product models shrink-swell susceptibility for individual building polygons in England and Wales. Neither is a geotechnical investigation or a diagnosis of building movement.
Read the map at the scale and coverage it was designed for
GeoSure is a 1:50,000-scale set of geological susceptibility data. Its six themes are collapsible deposits, compressible ground, landslides, running sand, shrink-swell, and soluble rocks; debris flow is a separate model. The map can support early planning, but its scale cannot show the ground conditions under an ADU foundation. Check which product, theme, geography, and licence applies; access terms differ across BGS products.
The PSA product uses building polygons and combines shrink-swell geology with factors such as foundation depth, drainage, building type and storeys, and nearby trees. Its overall score is on a 1–100 scale, with individual factor scores on 1–10 scales. A postcode result is an average across buildings in that postcode, not a score for the specific home. The catalog reports updates as needed, so its modification date is not a measurement date for a property.
Decide what the result can support
A susceptibility score does not prove subsidence, identify its cause, predict future damage, or describe foundation condition. If a result, visible movement, site history, or proposed excavation raises a concern, ask the planning authority and a qualified geotechnical or structural professional what investigation fits the site and proposed design. Keep the map, building identifier, product version, and any professional findings together.
GeoSure covers Great Britain; the PSA product described here covers England and Wales. Do not infer a Northern Ireland result from either product. See coal-mining checks for home improvements for a separate route in former coal-mining areas and the broader site-constraint guide for other hazards.