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International guidelines for limiting exposure to electromagnetic fields set out basic restrictions and reference levels to protect human health. To ensure compliance with these guidelines, standard measurement procedures must be used, and assessments of the uncertainties in the measurements must be reported. Nevertheless, neither the exposure restrictions nor the technical assessment standards specify how the measurement and computation of the uncertainties should be considered. This paper analyzes the following two sources of uncertainties that are not often considered in the assessment of exposure to electromagnetic fields: 1) repeatability and 2) spatial interpolation. For this purpose, electric field measurements were made in an area in which three medium-wave radio broadcasting transmitters are located. Systematic random sampling was performed with a spectrum analyzer and a monopole-type antenna, and geostatistical techniques were used to construct contour maps of the electromagnetic radiation and its associated uncertainties. The results suggest that, in handling uncertainties in assessments of human exposure to electromagnetic fields based on spatial interpolation from point measurements, based on medium-frequency amplitude modulation broadcast transmitters, the additive approach (i.e., the uncertainty is added to the results of the assessment before the exposure level is compared to the relevant limit) is the most appropriate.