After the Nguyen dynasty (est. 1802) founded their Vietnamese empire in Hue, the Red River Delta became one of two rice baskets (the other being the Mekong Delta) sitting at the end of a long pole. Thus, the Red River Delta, and northern Vietnam, were incorporated into a Vietnamese national space, or geobody, that deemphasized the delta's ties with southern China clear in borderland and Sinosphere geographies. Another result of establishing the Nguyen dynasty in Hue was the demotion of Hanoi, and its accompanying markets, to regional significance. A representation of this national space is the following excerpt from a 1838 map. In this partial reproduction, northern Vietnam is at the top and Hue is at the bottom. This map uses the derogative “An Nam” or pacified south, rather than the names “Đại Nam” or “Yuë Nan” as mentioned in the page on the Red River Delta in the Sinosphere. It is possible that this map's European makers did not appreciate the different implications of these terms.
Look at any map of Vietnam today and you'll see a representation of northern Vietnam in an S-shaped view of national space.