受传统地图学的影响，目前几乎所有的GIS和数字地图都是沿用传统的地图投影理论，在把椭球面坐标转换到平面坐标的过程中，将不可避免的产生位置、方向和面积等方面的变形。为了形成一副完整的地图，往往需要使用数学手段对经纬线进行压缩或拉伸，其中就包括使用许多改正数来解决平面坐标与实际实体几何位置的差别。在编制地图时，为了使区域范围内的投影变化最小，不同的国家和地区往往选用不同的投影方法，这就造成国家或地区之间的数据难以衔接。传统地图将投影作为自己参照系的空间数学基础，这在特定用途、局部范围内是可行的。当地图所表达的范围从小区域扩展为大区域或全球时，传统的投影已不能满足数字地球连续多分辨率和全面用途的需要。 杨永崇教授提出在椭球面上基于大地坐标进行数据集合，并在椭球面上数字成图表达地表对象的设想。在计算机中按照参考椭球体的形状和大小制作球面，将制图区域内的地球表面对象表达在其上，制作椭球电子地图。 基于此理论，本文着重于从小比例尺地图上，提取地理坐标数据。本文使用南方cass软件，并分别根据西北五省的扫描地图建立独立坐标系并对图像进行矢量化，在相邻省份的数字化地图上选择公共点，再分别求得公共点的地理坐标，并进行对比检验，以此来确定数据的可使用性。以此种方式作为椭球面电子地图的数据源。

Be affected of the traditional cartography, almost all GIS and digital maps are using the traditional map projection theory. In the process of the ellipsoidal coordinates convert to plane coordinates, it will inevitably produce position, orientation, size and other aspects of deformation. In order to form a complete map, it is often necessary to use mathematical means to compress or stretch the latitude and longitude lines, including using many corrections to solve the difference between the plane coordinates and the actual physical geometrical position. In preparing the map, in order to make the area within the projection minimal variation, different countries and regions often use different projection methods, which resulted in data between countries or regions are difficult to cohersion. The traditional map take projection space as their mathematical reference base, which is feasible in certain applications, within the local area. When the scope of map expression ranging from small regional extended to large regional or global, the traditional projection can not meet the needs of continuous multi-resolution digital earth and comprehensive. Professor Yang Yongchong proposes to collecte the data based on the ellipsoid geodetic coordinates, and the idea of digital mapping expressing the surface of the object on the ellipsoid surface. In the computer, in accordance with the shape and size of reference ellipsoid making spherical, the earth's surface object in the drawing area expressed on it, to make ellipsoid electronic map. Based on this theory, this paper focuses on the small scale of the map, to extracte geographic coordinates data. This article uses the South cass software, and according to the scanned map which based on the five northwestern provinces to establish an independent coordinate system and vector images. Choose a common point in neighboring provinces on the digital map, work out geographical coordinates of the common points, and conduct comparative test in order to determine data usability. Take this way as the data source of ellipsoid electronic map .