Altimetric maps are especially reliable as they are unaffected by the presence of clouds:
A difference in altitude generates a force that pushes water from highest level to lowest level. Due to Coriolis force, each horizontal force is linked to a current called “geostrophic current” that is orthogonal to the axis of this difference.
Away from the equator, sea anomalies described by bumps and holes in altimetric maps generate currents that rotate around highs and lows at the ocean surface, just like winds rotate around high and low pressure areas, in the atmosphere.
Geostrophic currents showed by altimetric maps enable to precisely highlight strongest frontal areas that are more favorable locations of high marine productivity.