The magnetic field satellite Magsat obtained total field data over almost the whole of the earth. We have studied these data in two different ways. The first way was to use spherical harmonic coefficients. It is often believed that these coefficients can be separated into those originating within the core of the earth and those from the crust at about degree 13 because of the change in slope of the power spectrum. Using coefficients above degree 13 (in two different representations), we have shown that there is little latitudinal variation of the source function and that the continent to ocean source function ratio is almost unity. We suggest that these unlikely observations are in reality due to the possibility that much of the signal carried in coefficients above degree 13 may originate within the core of the earth. If this is true, it is then possible to keep the energy external to the core of the field generated within the core at a constant even though the dipole field has varied in strength by a factor of 3 over the past 104 years. We have also produced models of crustal magnetization using the 2° × 2° average anomalous field and have shown how it is possible to obtain a physically meaningful susceptibility model, in which magnetizations are always positive. This is done by using an annihilator, which is a magnetization distribution within a spherical shell which produces no external field. The use of an annihilator is also appropriate for many problems connected with oceanic basins. Since present‐day oceanic crust is everywhere less than 180 Ma, the average magnetization seen at the altitude of a satellite is either zero for crust which is produced during times of rapid field reversal or positive for crust produced during times of constant normal polarity. Some results from continental and oceanic areas are discussed in the light of applying an annihilator.