We show that a global distribution of small scale heterogeneities in the lower mantle induces both frequency splitting and amplitude scatter of low angular order modes. These effects can be used in order to map the global distribution of small scale structures in the mantle, such as plumes. Two independent datasets, consisting respectively of lower mantle modes interaction coefficients and of observed amplitudes of core modes, can then be used to constrain the low angular degrees of the spatial distribution and the mean size of heterogeneities, allowing us to constrain the mantle structure of different scales. If these heterogeneities are assumed to be plumes associated with hotspot activity, the mean size of plumes obtained using the two datasets is then in good agreement with that obtained from geodetical or numerical convection studies. ¿ American Geophysical Union 1990