[en] In 1979, when the problem of high radon daughter levels in Swedish houses became widely published, the need for information on variations in the natural radiation environment became very apparent. The radon problem was at first attributed to radon emanation from alum shale based aerated concrete, but it was soon obvious that ground with an abnormally high uranium content constitutes an even greater risk for high radon daughter levels in houses. The geological Survey of Sweden was commissioned to produce a documentation in map form for all areas and rock types with gamma ray levels exceeding 30 μR/h, with the intention of delimiting risk areas for high soil gas radon contents. The maps, known as GEO-radiation maps, are produced at scale of 1:50 000. They are based primarily upon radiometric surveys, ground measurements of gammaradiation and geological mapping. To date some 450 map sheets have been published covering approximately 55% of the country. The maps provide primary information to local planning, health and building authorities as to variations in the natural radiation environment. Within the so-called risk areas marked on the maps, local authorities are recommended to investigate the soil gas radon content prior to any new development. Geological environments known, in Sweden, to be associated with radon daughter problems in dwellings are alum shale, a Cambrian, uranium-rich black shale, uranium-rich granites and uranium-rich pegmatites. Both alum shale and uranium-rich granites constitute extensive areas of bedrock. More recently it has been established that high soil-gas radon concentrations are also associated with glacial eskers. (Author)