The increasing of the engineering surveys’ volume necessary for the building of various large industrial facilities, demands rectification of many algorithms and techniques of mapping construction and operation areas. Such objects are, for example, linear structures – roads, railways, power lines, pipelines. A large-scale map must accompany the construction and exploitation of dams power stations, excavations, objects of urban infra-structure, etc. Many of the objects that require geodetic surveys are located in the piedmont and even mountainous terrain. In most cases, special algorithms of geodetic projections used do not take into account the altitude of the locality. Hence, it is necessary to consider the elevation of the mapped terrain. This article presents the results of the analysis of the significance of the introduction of the secant (additional) ellipsoid for solving the problem of reducing distortion when projected on the plane of the lines and coordinate points in mountain localities. The basic formulae that allow specifying the algorithms of geodetic projections with the height of the site. The results of computing experiments confirming the proposals for technological improvements of algorithms of geodetic projections. The basis of improvement is the use of a scaling factor reflecting the change in semimajor axis of the ellipsoid.