This invention relates to improved techniques for processing potential field measurement data from airborne surveys such as gravity surveys, and to improved techniques for data acquisition which are enabled by the improved data processing techniques. We describe a method of processing measured potential field data from a potential field survey of the earth to determine map data for mapping said field, the method comprising: inputting said measured potential field data, said measured potential field data comprising data defining a plurality of potential field measurements and associated positions, each said position defining a position of a said potential field measurement in three dimensions; determining a plurality relationships between said potential field measurements and said positions, each said relationship relating a said potential field measurement to a function of a said associated position in three dimensions multiplied by a field mapping parameter; and determining a substantially self-consistent set of said field mapping parameters for said plurality of relationships to thereby determine said map data.