Space scanning with a narrow gamma beam in several positions in the plane cross-section of a tested equipment provides the information on bulk densities on the basis of which the values of solid particles local concentrations can be evaluated. The approximative functions appropriate for the description of the local concentrations in a plane are chosen in dependency on the character of the measured system, usually in the form of polynomial, containing a selected number of constants. The values of these constants are determined from a set of algebraic equations which are derived from the approximative functions. The accuracy of the computation depends on the conditionality of the set of these equations. The suggested method of the evaluation determines the optimal number of constants in the approximative functions. The necessary number of scannings in one cross-section is discussed. The method has been applied for the evaluation of the space distribution of solid particles in two systems i.e. the mechanical mixing of suspensions which can be considered as having a symmetrical concentration distribution and the fluidization of powders which can be considered as having an arbitrary concentration distribution.