Technology for determining a geographical location is described. A sequence of magnetic field gradient measurements can be identified for specific positions on the Earth that correspond to a path traveled by a moving platform. The sequence of magnetic field gradient measurements for the path can be compared to a reference magnetic field gradient map. A trajectory derived from the reference magnetic field gradient map that correlates to the sequence of magnetic field gradient measurements can be identified. The trajectory can have known geographical coordinates. The geographical location of the moving platform can be determined based on the known geographical coordinates of the trajectory.