A survey of over 1000 homes in Fairfax County shows that a portion of the homes (1 in 5) have dangerous levels of indoor radon air pollution. Theoretical considerations and soil chemistry show that this can be attributed to significant quantities of Rn-222 progenitors in the earths regolith. Comparison of survey home locations with the published Fairfax County total gamma aeroradioactivity map shows that aeroradioactivity data are very successful in terms of identifying the "indoor radon potential" of local communities. The aeroradioactivity map is more successful than a recently published map, based mainly on soil types, that is distributed by the Fairfax County Health Department and is often used by Fairfax County realtors to estimate radon hazards. Airborne gamma-ray spectrometry is likely the best method for making radon hazard maps because it is comparatively quick to construct, inexpensive, and accurate.