In the light of the practical need of calculating the volume of snow all the year round in the region of Xinjiang

by means of a landsat image map .the problem is solved of how to draw automatically the useful parts of an area on the comprehensive image

the one of the same region and different size

in the system of the digital image processing; of how to delete the other parts of the area unconcerned.In this paper a datailed description is made of their principle and methods. Here are illustrations and the calculation patterns

and the applied technical process are given. The method may also be applied to Other technical image processing which is confined to some local regions of digital landsat image. It can find its application to the common kind of digital process syStem or analysis system.