Every city has a story hidden beneath its surface, shaped not just by people but by ancient landscapes and geological forces too. Under our streets, buildings and parks lies an unseen subsurface that has a major influence on how our cities function, grow and adapt.

On World Cities Day, we are highlighting urban geoscience — the study of the ground beneath our towns and cities — and why understanding this hidden world is essential for building safer and more resilient urban environments.

What is urban geoscience?

Urban geoscience helps us to understand the geology and both the natural (for example, ancient river valleys and glacial deposits) and human-made features (for example, old mine workings) beneath our cities. This knowledge helps planners and decision makers to more safely utilise the subsurface — for example, for water, energy and — while avoiding any challenges caused by the complex and sometimes unpredictable geology beneath our feet. As cities develop, urban geoscience offers the insight needed to mitigate risk and plan with confidence.

Examples of how British cities are influenced by geology

There are countless ways in which geology influences the evolution of our towns and cities. Here are four examples from around Britain.

London: shrink–swell clay and the changing climate

Much of London is built on the . This unit has clay-rich deposits that expand when wet and shrinks when dry, a phenomenon known as shrink–swell. This movement can cause cracks in buildings, damage roads and disrupt underground utilities.

With climate change, hotter and drier summers followed by intense rainfall are worsening the effects of shrink–swell. The 51ÁÔÆæ GeoClimate dataset models how these risks may change over time, showing areas most likely to experience future subsidence. Such modelling can allow for preventative or mitigative steps to be put in place to alleviate the effects of the hazard on property and infrastructure.

Glasgow: mining and geothermal energy

Glasgow sits on the Carboniferous-aged and the coal mined from beneath the city powered its industrial growth. The old mine workings have left voids in the subsurface that can collapse and, if the collapse is close to the surface, cause subsidence. However, if potential issues are known, preventative measures can be put in place to reduce the risk.

The 51ÁÔÆæ Mining Hazard dataset helps identify areas where past underground mining might pose a risk, supporting safer planning and development. Old mine workings are also providing new opportunities as warm water in flooded mine workings can be used to supply low-carbon heat and hot water to offices and homes, turning a legacy of coal mining into a .

Truro: radon risk from granite

Truro in Cornwall is a city built on Carboniferous to Permian-aged granite intrusions, which were formed when molten rock slowly cooled deep underground. Granite contains small amounts of the radioactive element uranium, which naturally breaks down (via a series of intermediate, unstable elements) over millions of years to produce radioactive .

In enclosed spaces like homes and offices, radon may build up to levels that pose a health risk, with prolonged exposure to elevated levels of radon increasing the risk of lung cancer. For most people, the risk of developing lung cancer from exposure to radon remains low. However, the advises you to test your home if you live or work in a radon affected area and there are several methods of reducing high radon levels in buildings.

Cornwall is just one of several areas around the UK were radon gas needs to be considered. The 51ÁÔÆæ/UKHSA Radon Potential dataset shows where elevated radon levels are most likely, showing where testing and mitigation are needed around the UK to make homes safer.

Cardiff: complex ground and urban redevelopment

The combination of river sands and gravels, glacial deposits and rocks of the Triassic-aged beneath the city of Cardiff affect drainage, groundwater flow and how easily the ground can be built on. As the city continues to grow and redevelop, understanding the subsurface is key for managing groundwater, avoiding subsidence and planning safe infrastructure.

The 51ÁÔÆæ 3D urban geology model for Cardiff helps to visualise the deposits beneath the city, while the 51ÁÔÆæ Civils dataset provides practical information on ground stability, excavation difficulty and chemical risks to construction materials.

Every city around the world is shaped or influenced to some degree by the rocks that lie beneath its foundations, a changing coastline along its shore or the risks posed by geohazards such as earthquakes, landslides or radon. As cities continue to grow and face new challenges, from a need to become climate resilient to an increasingly crowded subsurface, understanding the ground beneath them becomes more important than ever.

Urban geoscience connects the past with the present, helping us build cities that are not only functional but also resilient.

The update to the radon potential map of Great Britain, produced by the UK Health Security Agency (UKHSA) and BGS, is the first in over 10 years and provides an authoritative analysis of the likelihood of a building being in a ‘Radon Affected Area’ (an area with higher radon potential). 

Radon (chemical symbol: Rn) is a colourless and odourless gas that 1100 lung cancer deaths per year are attributed to in the UK. The risk is highest among smokers and ex-smokers.

For most people, the risk of developing lung cancer from exposure to radon remains low and levels of radon have not increased across the UK. However, UKHSA advises you to test your home if you live or work in a Radon Affected Area. There are several methods of reducing high radon levels in buildings.

The latest update to the , available to view on the , is the product of years of new analysis and research, combining the latest geological mapping with one of the largest databases of in-home measurements ever compiled. 

Whilst the vast majority of buildings remain outside Radon Affected Areas, this new map has refined our knowledge of areas where high radon levels are more likely to occur. The overall number of buildings with high radon levels remains the same.

The radon map allows local councils, national and regional governments, social and private landlords, private homeowners and employers to assess the radon risk in their properties. It is also used in building regulations to inform where radon preventative measures should be incorporated in new buildings.

While the vast majority of buildings remain outside Radon Affected Areas, if the property you own is in an affected area, it is important that you arrange for a test. If you live in private or social rented accommodation, speak to your landlord, who should organise a test for you to carry out.

Employers can use this map to help undertake a suitable and sufficient risk assessment and take appropriate action where necessary.

The updated maps provide information that allows property owners, landlords and employers to make informed decisions on the benefits of undertaking radon measurements and potential remediation work.

Tracy Gooding, principal radiation protection scientist at UKHSA.

Radon occurs in all rocks and soils. Using a revised statistical approach to our mapping of geology across Great Britain has enabled us to model where this geohazard is more likely to be present in buildings.

This map is a significant update to the previously published version and will help to raise awareness about this geohazard.

Russell Lawley, BGS Principal Geologist.

UKHSA has published . Further information on of radon are also available.

Radon data available through BGS

• A GIS compatible version of the indicative atlas is available to download free of charge on the BGS website.
• The definitive atlas is available at 25m resolution and can be licensed for use within a GIS. Further information on costs and limitations of use are also available on the Radon Potential dataset webpage.
• Individual property probabilities can be found either from a or by obtaining a . For large property portfolios a property risk assessment can be undertaken. Further information is available on the website.