The Relief Degree of Land Surface in China and Its Correlation with Population Distribution
中国地形起伏度及其与人口分布的相关性

The relief degree of land surface (RDLS) is an important factor in describing the landform macroscopically. Under the new proposed concept, based on the macro-scale digital elevation model data, by using ARC/INFO software, the RDLS of 10km×10km grid size is extracted and mapped in China. Then this paper systemically depicts the distribution rules of RDLS in China and its correlation with population distribution by analyzing the ratio structure, spatial distribution and altitudinal characteristics of the RDLS. The distribution rule is elaborately expatiated in three separate ways: the ratio structure, the accumulative frequency, and the change along with the longitude and latitude, which clearly reflects the regional topographic framework of China. The result shows that the majority of the RDLS is low in China, for more than 63% of the area in China with the RDLS lower than 1 (relative altitude ≤ 500 m). As for the spatial distribution, in general, the RDLS of the west is higher than that of the east and so is the south than the north. Specifically, the Hengduan Mountains and the Tianshan Mountains regions have the highest RDLS, while the Northeast China Plain, the North China Plain and the Tarim Basin have the lowest ones. The RDLS of 28oN, 35ooN and 42oN as well as of 85oE, 102oE and 115oE accords well with the three topographic steps in China. The RDLS of China decreases with the increase of longitude and the change clearly illustrates the landform characteristics that most of the mountains are located in the west and most plains in the east of China. The RDLS of China decreases with the increase of latitude as well and the trend shows that there are more mountains and hills in South China and more plains and plateaus in North China. In the vertical direction, the ratio of high RDLS increases with the increase of altitude. Finally, this paper analyzes the correlation between the RDLS and population distribution in China and the result shows that the RDLS is an important factor affecting the distribution of population and most people in China live in low RDLS areas. To be more specifically, where the RDLS is zero, the population amounts for 0.83% of the total; where the RDLS is less than 1 (relative altitude ≤ 500 m), the population reaches 20.83%; where the RDLS is less than 2, the population amounts for 97.58% of the total; and where the RDLS is bigger than 3, the population only amounts for 0.57%. That is to say, more than 85% of the population in China lives in areas where the RDLS is less than 1 and less than 1% of the population lives in areas where the RDLS is bigger than 3. The correlations between the RDLS and population distribution of eight regions in China are different. The correlation is obvious in northeast, north, central and south China, while it is nearly nonexistent in Inner Mongolia and the Qinghai-Tibet region.