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Different geographical environments,good or bad,have always affected the survival and development of human beings. Salt is an important substance closely related to human survival. The distribution of salt resources and the history of humans' discovery and utilization of salt cannot evade the constraints from the natural environment.
From the exploitation and utilization of salt well resources in Erhai region,the distribution of the origin of salt wells and their geographical locations have been relatively stable. Since they were discovered,most salt wells have not changed much in space,with relatively stable geographic locations. Differences of the natural environment such as the complex topography and geomorphology in Erhai region leads to the difference in discovery time and development level of salt wells in Western Yunnan. Because of these difference in the micro geographical environment,the distribution of salt wells and the salt well culture arising therefrom have their own characteristics. Based on this,it is highly important to study the distributional structure of salt wells and to explore and understand the relationship between the geographical environment and the salt well land in Erhai region,for the purpose of studying the salt well culture in Erhai region.
In Erhai region defined here,salt wells are mainly distributed in Dali City,Eryuan, Jianchuan, Heqing, Weishan, Xiangyun, Midu, Binchuan, Yangbi,Yongping,Yunlong,Lanping and other counties.
Located in the southwest corner of China,Erhai region has a special topography and landforms. It has greatly affected the historical development process of Dali region. In Erhai region,the 26°N line is an extremely important demarcation line. It not only divides the obvious differences of natural landforms in this region,but also further divides the differences of human social development in Yunnan Province. With this line as the boundary,in the north to the 26°N line,there are mountains with altitudes of more than 4, 000 meters,such as Gaoligong Mountain,Nushan Mountain,Daxue Mountain and others. Among them there are longitudinal currents of Nujiang River,Lancang River,Jinsha River and Yalong River. The elevations of the river valleys are mostly between 1, 500 and 2, 000 meters. There are huge altitude differences between mountains and valleys,with a height difference of thousands of meters. As a result of geological movements,these mountains and rivers crisscross with each other,forming Hengduan Mountains with parallel arrangements of high mountains and deep valleys. This kind of landform,different from those famous mountains and rivers on the Han land,is a unique geological feature of Erhai region.
In the southwest of China there is a vast planation area. As a large area preserved in the south to the 26° N line in Yunnan Province,it was named "Yunnan Plateau Surface". On this plateau,except for a few peaks exceeding 3, 000 meters,the mountain height gradually decreases,and the relative height between the mountains and valleys also decreases. The whole plateau inclines from north to south. In Xiangyun and Nanhua(with altitudes of 2, 200 to 2, 600 meters)in central Yunnan,it inclined to the east,west and south. At the border of Yunnan,it dropped to 1, 800 to 2, 000 meters above sea level. On the plateau,there are many differently sized basins suitable for population reproduction and agricultural production. They are known as"dams",which are the cradles of farming and animal husbandry culture and market town culture in Yunnan's society. In terms of the climatic conditions,most areas of Yunnan today belong to the western tropical monsoon climate zone,with the 28°N line as its northern boundary. The north to this boundary is characterized by a high-cold climate,while the south to the boundary is featured by a subtropical mountain climate. However,"the Kunming quasi-stationary front"from the Zhaotong － Qining － Xingyi line at the border of Yunnan and Guizhou makes the climate of Yunnan different from east to west. "The Kunming quasi-stationary front"is an important dividing line of the natural geography in China. The eastern area to the front is rainy in winter,while the western area to the front with Yunnan Plateau is warm and sunny in winter. All these have affected the social and economic development of Yunnan
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It is precisely because of the complex geological and geomorphological characteristics of Hengduan Mountains that those plain areas suitable for human survival and agricultural development in other areas of China are changed into anomalies in the north to the 26°N line in Yunnan Province. As a result,the population,economy and market towns of Yunnan Province mostly develop better in the south of the 26°N line than the north thereof. The 26°N line is the boundary between the high mountains and deep valleys landform of Hengduan Mountains and the Yunnan Deplanation Plateau. It lies on the edge of the Qinghai-Tibet Plateau. The 28°N line is the northern boundary of the western tropical climate zone. The north to the line is cold. Thus,between 26°N and 28° N,it reflects the characteristics of the transition from the subtropical mountain climate to the alpine frigid climate. On terms of the topography and physiognomy,it shows the transition from the high mountains and longitudinal valleys to a relatively flat plateau planation plane. These characteristics gave rise to an economic zone which has been lasting till now,that is,the human economic activities are concentrated in one zone with alternating agriculture and forestry and animal husbandry. In the north to the 28°N line,it is mainly forestry and animal husbandry. To the south of the 26°N line is mainly agriculture. In the area between 26° N and 28° N,economic activities are characterized by alternating agriculture and animal husbandry. It can be imagined that these geographical factors would obviously affect the social development of different regions in Yunnan.
Salt wells in Erhai region are mostly located to the south of the 26°N line,with only Jianchuan and Heqing County located between 26°N and 28°N. (Jianchuan is on 26°30'N while Heqing on 26°36'N. )Their formation and development were obviously influenced by the boundary and transition zone.
In addition to the geographic dividing line of the 26°N line,in Erhai region,the line from Luoping Mountain starting in the south of Jianchuan County to Diancang Mountain in the west of Dali is an important north-south vertical geographic boundary
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In the east to the Luoping Mountain-Diancang Mountain line,the terrain isrelatively gentle,with larger and more dams. There are also lakes such as Erhai Lake,Jianhu Lake and Zibi Lake,which are suitable for the development of agriculture,thus forming an important agricultural area in Erhai region. This area is home to nine of the 12 cities above county level in the administrative area of Dali Prefecture. Compared with the gentle basins and quiet lakes in the east,the geographical environment in the west to the boundary is at a disadvantage in terms of the conditions for human survival and urban formation and development. Of the 12 county administrations in Dali Prefecture today,only three are in this area. It is highly obvious that the differences of geographical environment between the east and west to the Luoping Mountain-Diancang Mountain line are an important reason for this difference.