The optimum Conventional Terrestrial System (CTS) can be defined by accurate coordinates of some number of stations distributed homogeneously all over the world. There are scores of laser and VLBI stations whose coordinates are known with high accuracy of the order of 1-2 cm. There are many CTS defined by the sets of station coordinates determined in the process of determination of the Earth rotation paramaters and the Earth gravity field. Presently existing stations are not distributed homogeneously on the Earth. They are located mostly in Europe and in North America. In this situation, the errors of orientation of axes and origin positions are not equal. Some of them, based on a small number of not homogeneously distributed stations, are not well-defined (stable).