[en] The spatial scale over which radon varies is usually unknown, and so efficient sampling schemes and methods of mapping cannot be selected. To determine the spatial scale of radon variation in the English Midlands the authors sampled radon in the soil using an unbalanced multistage scheme. The sampling design had seven stages representing distances between sampling points from 10 m to 7.5 km, increasing in a three-fold geometrical progression over an area of 225 km². The results indicate clearly that over 90% of the variation occurs over distances less than 10m. (author)