地球椭球体表面是曲面，而地图通常要绘制在平面图纸上，因此制图时首先要把曲面展为平面。然而球面是个不可展的曲面，如果把它直接展为平面时，不可能不发生破裂或皱纹。若用这种具有破裂或褶皱的平面绘制地图，显然是不实用的，所以必须采用特殊的方法将曲面展开，使其成为没有破裂或褶皱的平面，于是就出现了地图投影理论。
其基本原理就是：因为球面上一点的位置决定于它的经纬度，所以实际投影时是先将一些经纬线的交点展绘在平面上，再将相同的经度的点连成经线，相同的纬度的点连成纬线，构成经纬网。有了经纬网以后，就可以将球面上的点，按其经纬度展绘在平面上相应的位置处。
许多分析技术和空间数据都是针对二维坐标或平面坐标设计，以平面地图投影的方式来存储空间坐标，因此很多时候我们都需要利用地图投影将三维的地理坐标转换为平面坐标。所谓的地图投影就是通过特定的数学方程式将经纬坐标（λ，φ）转换为平面坐标（X，Y）。从三维坐标转换为二维坐标时总会出现扭曲变形，地图投影就是用来减小这种变形的。
本文对地图投影变换做了尝试性的分析研究，利用VC++编程语言实现了斜轴等积方位投影、墨卡托投影和高斯-克吕格投影三种投影变换，并做了应用测试。
Earth is an ellipsoid and its surface is curved, but the maps are usually drawn to the floor plan on paper. So before drawing you must spread the curved surface surface to the plane first. But a spherical surface can't be spreaded, it can't be braken or no wrinkle if you direct spread it to the plane. It's obviously that it's not practical if you use such broken and wrinkled plane mapping. So we must adopt special methods to spread the curved surface, which is called map projection theory.
The basic principle of map projection theory is: Because a point in the ball surface decides its latitude and longitude, so in the actual projection, spred and draw the intersection point of of latitude and longitude lines on the the plane, then line the points with same longitude into Longitude lines, and line the points with same latitude into latitude lines, finally compose the latitude and longitude network. Now the points of the ball can be drawed on the plain according to their own latitude and longitude.
Many analysis technology and space data are designed by the two-dimensional coordinates or plane coordinate, and used plain map projection methods to storage space coordinates, so many times we all need three-dimensional map projection to convert 3D geographical coordinates into the plane coordinates. The so-called map projection is using a specifically mathematical formula toconvert latitude and longitude coordinates (λ, φ) into a plane coordinates (X, Y). Coverting the three-dimensional coordinates into two-dimensional coordinates will take place twist deformation, and map projection is methods to reduce this deformation.
This paper studies and analyses the map projection transformation, using VC + + programming language to realize three projection transformation: inclined position projection, Mercator projection and Gaussian M- Ke Lvge projection, and makes the application tests.
