On harmonization of radon maps

Background: Maps are important tools for geographic visualization of the state of the environment with respect to resources as well as to hazards. One of the hazards is indoor radon (Rn), believed to be the most important cause of lung cancer after smoking. In particular, as part of Rn mitigation policy and in compliance with the European Basic Safety Standards, EU Member States have to declare areas with elevated indoor Rn concentration levels. However, as this is done by national authorities according to individually chosen criteria, the resulting maps are not easily comparable. Objective: We aim to identify causes for the lack of compatibility of maps and suggest solutions for the problem. Design: This study draws from experiences of recent research projects, literature, and personal involvement of the authors in the discussions. Results: An overview is given on causes and effects of lack of compatibility between maps. Existing experi- ences are reported. Options for defining lack of compatibility and for identifying it are discussed. Methods for harmonization, that is, remediating lack of compatibility, are addressed. Conclusions: The difficulty of harmonization increases with the aggregation level of data which support maps. Harmonization is the more difficult, the higher aggregated the data are which support maps. In particular, harmonization of radon priority area maps is technically non-trivial, and theoretical efforts as well as practical tests will have to be undertaken.