Why are Ningxia and Fujian so close?

During the Ming Dynasty, a large-scale immigration occurred in China! Most of them came from Shanxi, Ningxia, and northwest provinces and moved to southern provinces! In ancient times, remote areas in the south were sparsely populated, and it took many years of migration to open up the land in the south where no one was cultivating it! I don’t know much about Xiangtian’s situation! This is probably what it means, so many southerners are originally from Shanxi and northwest regions!