Because in 1845, Shanghai Daogong Mujiu and British Consul Pavel demarcated the first concession where foreigners lived. When they agreed on the "land charter" and delineated four boundaries, they set the eastern boundary at Yangjingwo (now Yan 'an East Road), which was translated into Chinese as "Huangpu Beach" and was then called Shanghai Beach.

As a seaport, Shanghai Town is booming, so it is necessary to set up a shipping company here, as mentioned above. But the rise of Shanghai from town to county has nothing to do with the rise and fall of its maritime trade. According to Huating County, before it left Shanghai, there were almost all the places on the south bank of Songjiang and seven counties, which were very prominent in the southeast, with more than 100,000 households (according to the geographical records of Yuan Dynasty, there were 164,000 households in Shunshi Huating and Shanghai County).

Extended data:

During the Tang and Song Dynasties, the coast of Shanghai expanded rapidly, rising by one mile every ten years on average. According to this calculation, the land formation in Shanghai Pu area should be before the middle of the 9th century. It is estimated that it was dug into a pool by coastal people at the end of the 9th century. As for calling this Pu Shanghai, it should be called Shanghai Pu after the downstream formation, because Shanghai and Shanghai are corresponding names. Without Shanghai Pu, there would obviously be no Shanghai Pu. It is estimated that its age may be at the beginning of 10 century.

From the end of 10, the maritime trade port on Wusong River was Qinglong Town (now old qingpu town). By the end of 12 or the beginning of 13, due to the shallow siltation of Wusong River, the port status of Qinglong Town was gradually replaced by Shanghai downstream. It was not until 1960s (13) that Shanghai officially became a seaport with a "city shipping company" and a town with local institutions.

References:

People's Network-The Disappearing Sanjiagang in Shanghai Beach