The joint PHE-GSNI-BGS digital Indicative Atlas of Radon in Northern Ireland presents an overview of the results of detailed mapping of radon potential, defined as the estimated percentage of homes in an area above the radon Action Level. The Indicative Atlas of Radon in Northern Ireland presents a simplified version of the Radon Potential Dataset for Northern Ireland, with each 1-km grid square being classed according to the highest radon potential found within it, so is indicative rather than definitive. The Radon Potential Dataset for Northern Ireland provides the current definitive map of radon Affected Areas in Northern Ireland. The Indicative Atlas of Radon in Northern Ireland is published in Z Daraktchieva, J D Appleton, D M Rees, K A M Adlam, A H Myers, S A Hodgson, N P McColl, G R Wasson and L J Peake, 2015. Indicative Atlas of Radon in Northern Ireland. PHE-CRCE-017, 22 pp. Radon is a natural radioactive gas, which enters buildings from the ground. Exposure to high concentrations increases the risk of lung cancer. Public Health England (PHE) recommends that radon levels should be reduced in homes where the annual average exceed 200 becquerels per cubic metre (200 Bq m-3), the radon Action Level. Public Health England defines radon Affected Areas as those with 1% chance or more of a house having a radon concentration exceeding the Action Level.