What principles did the "immigration and border consolidation" in the Han Dynasty follow?

Seo Woo in the Eastern Han Dynasty pointed out in "Please Reply to Three Counties" that the reason why the immigration work in Hexi and the Western Regions in the Western Han Dynasty was outstanding was that the immigration place he chose was very suitable for agricultural production: "Gong Yu is in Yongzhou, where the land is up and down, the fields are thousands of miles, and the crops are abundant. There is also the Qiuci Salt Pond of Huimin, which is rich in aquatic plants and the soil is suitable for animal husbandry. Cattle and horses with tails between their legs, sheep blocking the way. Because the canal was irrigated, the water was poured into the river, saving hard work and rations. Therefore, Emperor Xiaowu and Emperor Guangwu built Shuofang, opened Xihe River and set up a county, which is the same reason. " It can be seen that the government's macro guidance and planning can avoid the disorderly flow of immigrants and make the immigration work achieve greater benefits.