Simply, the units in which magnetic survey maps are often contoured. 1 gamma = 1 nanotesla. A unit for stating the magnitude of the magnetic field vector B represented by the number of lines of induction passing through a unit area perpendicular to the vector direction.

1 gamma = 10^-5 gauss

= 10^-5 lines/cm²

= 10^-1 line/m²

= 10^-9 weber/m²

= 10^-9 tesla = 1 nanotesla