A new method for determining the vertical interval of isotopographic surfaces on rugged terrain was developed. The method is based on the concept of determining the differentiated size of the vertical interval using spatial-statistical properties inherent in the modal characteristic, the degree of variability of apical heights and the chosen map scale. It was found that the morphometric characteristics of the terrain are highly informative, can serve as geoindicators, and have applied value; their calculation formulas were provided. An analytical assessment of the determination of differentiated sizes of the vertical interval was made. Its initial parameters are as follows: modal height, scale and variability of apical heights. The vertical intervals are differentiated by dividing the morphometric field of the terrain into two parts, the height in the contours whereof is lower (hi < hmo) and higher (hi > hmo) than the modal height, respectively; the reasoning behind the analytical assessment of the calculation of apical height variability and vertical intervals, which takes into account the peculiarities of terrain formation, was given; the main contour is drawn through the modal value of apical heights and then drawn through other contour systems based on the calculated vertical interval values, differentiated by the divided parts of the morphometric field.