The largely automatic mapping observed between space and sensory magnitudes suggests representation by a single system across domains. Using stimulus response compatibility tasks, the study confirms that a relative, auditory magnitude such as loudness shows a spatial compatibility effect similar to those evidenced for visual sensory domains but only with comparison tasks and for vertically oriented responses. No effect is seen when participants track changes in amplitude or when responses are oriented vertically. In a bimodal context, the study tested whether the spatial mapping of magnitude in 1 sensory modality (loudness) interacts with the spatial representation of magnitude in another sense (luminance). Observed interactions across modalities suggest overlap of magnitude representation across distinct sensory domains, whereas the absence of an effect for dynamic changes in loudness suggests that it is useful for decisions to act on 1 of several objects rather than for tracking magnitude changes in 1 object.