Automated Landform Classification of China Based on Hammond’s Method

The automatic classification of Macro landforms was processed with the program developed by Hammond’s Manual procedures, which based on properties of slope, local relief, and profile type, which consists of 5 landform types, 24 landform class and 96 landform subclasses. This program identified landform types by moving a square window with size of 9.8 km × 9.8 km. The data includes 816 sheets of topological map with a scale of 1:250,000. The DEM were buildup with the contours and mark points based on this data with a cell size of 200 m, and merge into one sheet. The automated classification was processed on this DEM data with a AML program of ArcGIS 10.X Workstation. The result indicates it produced a classification that has good resemblance to the landforms in China. The maps were produced respectively with 5 types, 16 classes and, 90 subclasses The 5 Landform types of landforms were Plains (PLA), 20.25% of whole areas; Tablelands (TAB) of 3.56%; Plains with Hills or Mountains (PHM) of 32.84%; Open Hills and Mountains (OHM) of 18.72%; Hills and Mountains (HM) of 24.63%. In the result of 24 landform classes, there are not some classes, such as irregular plains with low relief; open very low hills, open low hills; very low hills, low hills, moderate hills. The result of 96 landform subclass is similar to the 24 class.


Introduction
To some degree, landforms influence the distribution and evolution of ecology and other environmental factor, which is the core and the basic content of geography [1]. Landform morphological classification is the basic unit of landform, and also the first step in solving geomorphic problems. The landform classifications of large scale were started in 1950 in China. In 1956, the 1:4,000,000 Landform Clas-sifications and Region Planning Map of China, according to the altitude and surface cutting degree (Table 1). In 1979, the Mapping Standard of 1:1,000,000 Landform Classifications in China were completed, and classified the landform types with the altitude, relative altitude and the surface cutting degree, according to the classification schemes of З.A. Cварицевская (1975). Until 1989, only 15 sheets landform maps (1:1,000,000 scale) were completed. This mission was suspended for a long time. Until 2009, the 1:1,000,000 scale landform atlases of whole China is accomplished [2]. The two landform classifications schemes above, is based on manual process.
The 1:40,000,000's scheme is based on forms and exogenic forces, and many parameters are not quantitative. There were many quantitative factors is introduced into the 1:1,000,000's scheme, such as altitude, local relief, and slope. The local relief is classified into 4 classless, less than 500 m is low relief hills; 500 -1000 m is moderate relief hills, 1000 -2500 m is high relief mountains and more than 2500 m is very high relief mountains [3]. There are also some papers adopted local reliefs but different classes in whole China's landform scheme. Cai Zongxin (1986) classified grade into 5 classes, less than 20 m is plains; 20 -200 m is hills, 200 -500 is low mountains, 500 -1500 m is middle mountains and more than 1500 m is high mountains ( Table 2) (Table 3).
In 1990's, there are some scholars contributing to extracting the single landform parameters in China, such as ridge line and valley line [5] [6] [7], summit [8], shoulder line of valleys [9] [10], micro topography [11]. All above are based on the regions of simple landforms evolutions. There are many limits to automatically whole China's landform classifications. Liu Aili et al. (2006) [12] attempted to automate classify the landforms of whole China based on image classifications methods. But the sampling cell is 1000 m × 1000 m, which is coarse enough to omit many small landform units.   [2]. The computer-program is based on the approach developed by Dikau et al. [15]. In order to compare with the international landform maps, the parameters of Hammond's scheme are kept unchanged.

Concept
Hammond's hierarchic landform classification is based on properties of slope, localrelief, and profile type.
1) The slope is divided into 4 levels based on the percent of area gently sloping. If the inclination is below 8%, we call this gently slope (Figure 1). The percent area is calculated in moving widow (9.8 km × 9.8 km). 2) Local relief is the difference between maximum and minimum elevation in moving window. Local relief had a non-linear relationship with horizontal length by examining a variety of mountain belts [16]. Tu Hanming et al. [4]- [17] calculated the length scale with the sampling data from the whole land China, 5 optimum statistical length was calculated corresponding to different map scale, which is 2, 6, 16, 20, 22 (km 2 ). In this paper, we choose the 9.8 km × 9.8 km in order to compare with the Hammond's classification.
3) Profile type subdivide tablelands as upland units and plains with hills or mountains as lowland unit [15].
With these three parameters, Hammond classified 96 landform subclasses theoretically ( Table 4, Table 5). Hammond used only 45 subclasses were common in U.S. [18]. He generalized his results by merging areas smaller than 2072 km 2 into adjacent units to avoid cluttering at a 1:5,000,000 map. Dikau et al. [15] developed automated approach identified all 96 landforms units without generalization.

Method
The data were processed in ArcGIS 10.    Yun-gui Plateau. In Figure 2, Qinghai-Tibet Plateau is mainly classified into PHM; Mongolia Tableland and Loess Tableland is classified into PLA or PHM and the Yun-gui Tableland is classified into HMO. There are many hills or mountains in tableland in China. The basin is basically classified into PLA, but the Sichuan Basin is mainly classified into PHM or PLA.

Conclusion
Automated landform classification produced a classification that has good resemblance to those of manual approach. However, some classes are different from manual method. There are much more complex landform in China, and the geomorphologic evolution is much more different, so it needs to improve the method to classified more reasonable. Furthermore, the effects of scale and generalization also should be paid special attention.

Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this paper.