1:500万中国海陆地质-地球物理系列图编图范围广,包括中国陆地及所辖海域以及周边陆地和海域,共涉及8种地质、地球物理专业图.本文介绍了建立本次编图的数学基础即地图投影的过程,讨论了确定系列图投影方式及参数的原则和方法,选择墨卡托和兰伯特等角割圆锥两种常用的保角投影方式做试验,比较了在这两种投影之下系列图范围内编图重点区域,即中国的海陆疆界的位置姿态,长度和面积变形情况,最后选择了兰伯特正轴等角割圆锥投影,以105°E为中央经线,15°N,40°N为标准纬线.在综合考虑各专业编图数据要求和分幅最小化原则后,确定了矩形图幅四至坐标.采用这种图幅设计方案,中国大陆姿态端正,地质要素的形态和方向畸变小,重点编图区域长度和面积变形可控制在10%以内.

Geological-Geophysical map series of Chinas Land and Sea on the scale of 1:5 000 000 include eight geological and geophysical maps: Free-air gravity anomaly map, Bouguer gravity anomaly map, Magnetic gravity map, Moho depth map, Seismic Tomography Maps, Geological map, Tectonic frame map, and Tectonic evolution maps. The mapping area includes Chinese mainland and China seas and the adjacent land and sea area. This paper discusses the principal and method for choosing proper projection, which is the key question and mathematical base of GIS mapping. Based on the research of the former similar mapping and the understanding of the nature of different projections, we choose two common used equal-angle projections, i.e. Mercator and Lambert conformal conic projections for consideration. The deformation ratios of length and area are calculated under these two projections in the mapping area. The position and shape of Chinese land and sea boundaries are compared for testing different design solution of projection parameters. Lambert conformal conic projection is chosen finally not only because it causes less deformation, but also because it could limit the mapping area on a smaller scale which keep the map subdivision to a minimum. The central longitude of Lambert conformal conic projection is set to 105°E and the two standard parallels are 15°N and 40°N. The data requirement of different maps is also taken into account when setting the four corner points of the map. With this solution, Chinese mainland has a good visual effect, geological elements have small shape and direction deformation, and length and area distortion ratio can be controlled within 10%.