Analysis of the Difference between Surface Area and Vertical Projection Area on Shaanxi Qinling Mountains based on DEM

Based on DEM of Qinling Mountains, used the model of the center cell and the adjacent eight cells, we calculated the surface area of Shaanxi section Qinling Mountains. The results shows that: (1) The surface area of Shaanxi section Qinling Mountains is 75 224.67 km², which is an increase of 22.04% from the vertical projection area；（2）The relation between the difference of surface area and vertical projection area and elevation is parabolic. The altitude of 2 000 meters is the area with the largest difference between the surface area and the vertical projection area in Shaanxi section Qinling mountains；（3）Compared with the vertical projection area, the area of low mountains, medium mountains and submountains in Shaanxi section of the Qinling mountains increased by 2 301.54 km², 6 181.67 km² and 691.60 km² respectively, with the growth rate of 10.68%, 18.37% and 18.25% respectively.（4）The difference between the surface area and the vertical projection area is various in different land use types. Not using land is the largest, the difference is 34%. The second is forest land which the difference is 28%, and the lawn is approximately 20%. Difference is small in farmland, other forest land, water and residents and industrial land, which is 12%, 8%, 5% and 8% in turn.