Calibration of carborne gamma-ray spectrometry systems for 137Cs is carried out with a source successively placed at 791 positions within an area of 34m 62m. A computer model supplements the measurements. Hereby a sensitivity map for a surface contamination is generated as well as line and area sensitivities. Another model converts surface sensitivity to sensitivity for a deep contamination. Use of the sensitivity map for a non-homogeneous distribution of 137Cs is demonstrated. Applications of line sensitivities for special tasks are discussed.