AbstractPoints of maximum and minimum elevations together with points of curvature inflection are chosen in the field when executing levelling nets. Since these points are definite and crucial in defining the slope of the ground surface, they are used in a mathematical model for contouring. This method proves to be more rigorous than the usual linear interpolation. It also reduces the amount of field work required, since only those crucial points which define the ground shape are considered and, accordingly, the number of levelling points is reduced.