The coordinates of a nuclear spin relative to a lanthanide ion can be determined with high accuracy in a system, where a paramagnetic lanthanide tag is attached to a protein of known three-dimensional structure. First, pseudocontact shifts (PCS) of the protein are measured by NMR to determine the coordinate frame of the magnetic susceptibility anisotropy (DeltaChi) tensor associated with the lanthanide tag. Next, the PCS of the nuclear spin of interest is used positions it relative to the DeltaChi tensor. With lanthanide tags at three different sites, the position of the nuclear spin can be restricted in a way analogous to the global positioning system (GPS) of a mobile phone. Examples of this approach are shown for changes in amino acid side chain position triggered by metal binding and in response to ligand binding.