Description: The Radon data: radon potential dataset is the definitive map of Radon Affected Areas in Great Britain and Northern Ireland, created jointly by Public Health England* (PHE) and the BGS using long-term radon measurements made in over 479 000 homes across Great Britain and 23,000 homes across Northern Ireland (without affecting householders' confidentiality), combined with geological map data.The dataset includes a built in 75 m 'buffer', made up of 50 m to allow for the margin of error in the geological lines, and 25 m to represent the average extent of a home.PHE recommends that radon levels should be reduced in homes where the annual average is at or above 200 becquerels per cubic metre (200 Bq m-3) — this is termed the Radon Action Level.PHE defines Radon Affected Areas as those with one per cent chance or more of a house having a radon concentration at or above the Action Level of 200 Bq m-3.The radon potential dataset answers the following questions:Is a property in a Radon Affected Area?What level of Radon Protective Measures do I need to install if I am building a new building or an extension to an existing building?