Maintaining an inventory of state property as part of a unified federal information management in- formation system created in the prescribed manner by the RF Government requires accurate and correct calculation of the area, which corresponded to a geometric shape on a horizontal plane. To do this need to apply the surface of the ellipsoid, which is horizontal for all territories. But the calculations on the surface of the ellipsoid require a large amount of computation. We discussed the possibility of calculating the area of any site on the surface of the equivalent sphere. Results are completely consistent with the results,calculated on the surface of the ellipsoid, but requires less computation. In some cases, the error of calcu- lating the area on an equivalent sphere less than at the surface of the ellipsoid.