New global maps of the vector magnetic anomaly field of Earth are derived from Magsat data. Improvement on earlier published vector and scalar maps is achieved with the following procedure: (1) The noise level of vector measurements associated with the discontinuities of the in-flight sensor altitude determination is reduced by selecting the data. (2) A monthly model of the main field is computed to account for secular variation, using only quiet day data. (3) The time dependence of the ring current effect is taken into account using hourly values of the Dst index based on ground observations. (4) Sectorial indices based on ground observations are introduced to select profiles corresponding to low magnetic activity. These indices provide a better discrimination of quiet data than the global Kp index usually used for that purpose. (5) A time- and longitude-dependent dynamic model of the equatorial electrojet is derived and used to correct magnetic measurements at low latitudes. Anomaly maps of X and Z components are obtained using selected measurements within the reduced altitude range: 350--425 km. These maps are compared with earlier Magsat anomaly maps, and their respective resolutions are discussed. These maps evidence large anomalies of lithospheric origin within the oceanic domain. In particular, the Z map displays a characteristic pattern of long-wavelength anomalies in these areas. It is first shown that some of these anomalies, particularly in the North Atlantic and Indian oceans, may be correlated with the age of the lithosphere. Then, a significant similarity between magnetic and geoid anomalies above ocean basins is evidenced. This suggests that long-wavelength oceanic magnetic anomalies may also be attributed to variations of the thickness of the magnetized layer associated with ocean floor topography. ¿ American Geophysical Union 1990