『Abstract
　Canada is a vast country with most of the population living on a small portion of the land. However, for a national radon potential map, it is mandatory to cover the entire country including sparsely populated areas. Because of these characteristics, the radon map development for Canada is challenging. After briefly reviewing of radon map development in the world, this study considers a multi-tier approach to best use available however limited resources and to generate a national radon map in a timely fashion. In summary, radon potential maps for highly populated areas should be determined by direct indoor radon measurements where enough indoor radon data are available. In areas where indoor radon measurements are limited or not yet available the radon potential maps could be developed from various sources with a multi-factor scoring system including geological information on soil permeability, soil gas radon concentration and ground uranium concentration. In sparsely populated areas, radon potential maps can only be generated with geological predictive tools, especially in those areas where no houses have yet been built. because indoor radon measurement data and geological information relevant to radon are very limited in Canada, a multi-step strategy is also worth considering in addition to the multi-tier approach.

Keywords: Radon; ²²²Rn; Indoor radon; Uranium; soil gas permeability; Risk mapping』

Introduction
Brief review of radon potential mapping methods
　Direct measurement of indoor radon concentrations
　Geological radon predictive tools
　Multi-factor scoring system
Available data for radon potential mapping in Canada
　Indoor radon measurements
　Airborne gamma-ray spectrometry surveys
　Soil gas radon surveys
A multi-tier approach
Conclusions
Acknowledgments
References