Abstract: So far, there are many papers on how to establish a planar coordinate system. However, most of them have studied the establishment of a planar coordinate system in a small area. It's relatively simple. A planar coordinate system that meets the required precision can be established by using height compensation plane, translating central meridian or both. There are few researches on how to establish a planar coordinate system in a large area (nearly ten thousand square kilometers). This paper makes a detailed study on analysis and discussion this complicated problem, and obtains reasonable results. The method and process of induction can enlighten similar problems and can be taken as a reference.

Key words: length distortion, ellipsoid, elevation naturalization, Gauss plane, Gauss projection