Guanzhong Plain, also known as Weihe Plain, is located in the hinterland of China and is the birthplace of the splendid culture of the Chinese nation. From Baoji in the west to the Yellow River in the east, it is located in the middle and lower reaches of Weihe River. It is narrow in the west and wide in the east, with a width of about 1km in the west, 80 km in the east and 360 km in the east, covering an area of about 34,000 square kilometers. The plain is low in the east and high in the west, with an altitude of 325 ~ 750 meters. It was formed on the basis of Weihe graben in North China platform due to the continuous subsidence of the earth's crust and the acceptance of sediment accumulation. The southern part of the plain is adjacent to the Qinling Mountains. The Qinling Mountains are/kloc-0 ~ 40km wide from north to south and 200km long from east to west, with a general elevation of 1500 ~ 2000m, and the elevations of Zhouzhi, Huxian and Chang 'an are 2000m. The mountain ranges form a magnificent natural barrier in the south of Guanzhong. Guanzhong Plain is bordered by Weibei Beishan system in the north, and Beishan (Xiaolongshan) is the southern edge of the Loess Plateau, which is impacted by flowing water and the terrain is broken and rugged.

2. River

There are many rivers in Guanzhong area, most of which belong to the Weihe River system in the Yellow River basin, accounting for more than 90% of the whole area. Among them, the Weihe River traverses the central part of Guanzhong Plain, including 12 first-class tributaries, 85 second-class tributaries, 84 third-class tributaries and 50 fourth-class tributaries. The main first-class tributaries are Heihe River, Dagengyu River, Niyu River and so on.

Because there are many rivers and dense river networks in Guanzhong area, the terrain is high in the west and low in the east, which improves the favorable conditions for water conservancy construction. During the Qin and Han Dynasties, water conservancy projects in Guanzhong reached a climax, and water conservancy projects such as Zheng Guoqu, Caoqu, Longshou, Liufu, Baiqu, Guo Cheng and Menglong were successively built, forming a large-scale irrigation network in Guanzhong, which greatly promoted the development of agriculture in Guanzhong.

A large number of rivers and water conservancy projects provide ancient solutions to the problems of domestic water, palace environment water and grain transportation water.

Numerous rivers provide convenience for waterway transportation. In ancient times, the Weihe River was rich in water, and rivers below Xi 'an could sail big ships. During the Spring and Autumn Period, the famous "boating movement", the capital of the State of Qin transported grain to the State of Jin, and part of it was the Weihe River waterway. In the sixth year of Yuanguang, Emperor Wu of the Han Dynasty dug the Grand Canal on the south bank of Weihe River to divert water and deliver materials to Chang 'an. Yongtong Canal was built in Sui and Tang Dynasties.

In the spring of six years, Emperor Wu of the Han Dynasty established a military system on the south bank of Weinan, opened a river in Weinan and delivered food and other items to Chang 'an. During the Sui and Tang Dynasties, the Yongtong Canal was built.

3. Land

Due to the warm climate and suitable dry and wet conditions in Guanzhong area, aeolian loess and alluvial loess are widely distributed, and cinnamon soil is widely developed under the influence of deciduous broad-leaved forest vegetation. In addition, the agricultural development in Guanzhong area has a long history, and human activities have a far-reaching impact on the soil. On the basis of cinnamon soil, after long-term application of soil fertilizer, a thick mature layer is formed, which is called soil. It is a fertile soil with strong fertility.

Since ancient times, there have been thousands of fertile fields in Guanzhong, and the soil in Yongzhou, Shangshu, Gong Yu is yellow soil. The fertility rate was the highest in the country at that time. In the ancient society with personnel and agricultural economy as the main modes of production, soil fertility in various areas of the capital was paid considerable attention to because fertile soil was more suitable for farming. In the early Han Dynasty, Lou Jing pointed out that the land in Guanzhong was fertile and easy to cultivate, which was called Guanzhong Tianfu. The fertile soil in Guanzhong provides conditions for agricultural production and economic security for the capital.

4. Climate

Historically, the climate in China has experienced four warm periods and four cold periods. In the process of climate change, the climate in Guanzhong area has also changed accordingly, but on the whole, the climate in Guanzhong area is superior, warm and humid, with four distinct seasons since ancient times. This climate is conducive to the growth and development of crops and provides favorable conditions for the economic development in Guanzhong area. In addition, the cold and warm climate is more suitable for human survival.

5. Property

The hinterland of Guanzhong is an alluvial plain formed by Weihe River, Jinghe River, Luohe River and their tributaries. Fertile soil, pleasant climate, well-developed irrigation projects provide favorable conditions for agricultural production and rich agricultural products. In the northwest periphery of Guanzhong, animal husbandry is relatively developed, and geological tectonic movement makes Qinling Mountain rich in jade, gold, molybdenum, silver, copper, iron and other mineral resources, which provides a rich material foundation for the construction and development of the capital.

6. Population

In ancient feudal society, laborers were the basic social productive forces that could create material wealth and were the main targets of exploitation by rulers. There are many people and soldiers, and many people are in hard labor. Therefore, the population of a region is one of the factors that should be considered in capital construction.

Due to the lack of data before Qin and Han dynasties, it is difficult to verify the ancient population in Guanzhong area. Since the Qin and Han Dynasties, population statistics have been paid attention to, and the population is more credible.

Guanzhong area was a densely populated area in the Western Han Dynasty. According to Hanshu Geography, in the second year of Yuan Dynasty (AD 2), there were 647 180 households with a population of 2,436,360, with an average of 47 people per square kilometer.

During the Sui Dynasty, Emperor Wen unified the whole country, ending the turmoil of more than 200 years since the end of the Western Jin Dynasty, and the population also increased during this period. During the great cause years, there were 490,000 households in three counties of Guanzhong with a population of 2.53 million.

During the reign of Kaiyuan Tianbao in the heyday of the Tang Dynasty, the production was developed and the population was increasing. According to Geography of New Tang Dynasty, in the first year of Tianbao (AD 742), there were 9,049,490 households with a population of 48,49611. There are 790 households with nearly 4.4 million people in Shaanxi, accounting for one eleventh of the country's total population, more than any previous one.

The huge population in Guanzhong area provides a population base for the establishment of the capital city.

7. Agriculture and handicrafts

The mild climate, fertile soil and vast plains have created superior natural and geographical conditions for agricultural production. The construction of water conservancy projects in past dynasties has provided a guarantee for the economy here, making the agricultural economy in Guanzhong area quite developed, making it the richest area in the ancient world. "So the land in Guanzhong accounts for one-third of the world, but the population is only three, so it is rich and even ranks sixth." During the Tang Dynasty, the soil in Guanzhong was the most fertile in China. The Book of the New Tang Dynasty called it "Woye", which showed that Guanzhong's agricultural economy was very developed and provided a solid material foundation for the formation of the ancient capital.

Agriculture in Guanzhong area is developed, animal husbandry in the northwest periphery of Guanzhong area is developed, and the surrounding mountainous areas are rich in natural resources such as copper, iron, gold, silver and jade, which provide raw materials for the development of government and folk handicrafts and commerce. In addition, Guanzhong is located at the starting point of the "Silk Road", the east-west communication avenue, and its handicraft industry and commerce are very developed, which provides a material foundation for the construction of the ancient capital.