Abstract: For the integration of land use and planning work, this paper discusses the area difference in different urban coordinate systems and analyzes the theoretical law of area change from the ways of different ellipsoids, different Gauss projection planes and different central Meridians, using the formulas of gauss projection and height reduction. According to the actual situation in Ningbo, considering the central part of the city, the edge of the city and the high mountain area, the paper selects five representative survey areas. Based on the existing Ningbo city coordinate system and the national coordinate system, the paper compares the area difference under various conditions and points out the main reasons and explores the unified calculation scheme of urban area during the merging of different business sectors under the natural resources system.

Key words: urban coordinate system, height reduction, ellipsoid area, Gauss projected area, area of difference