How to explain the Central Plains in ancient poetry?

The word "Central Plains" has a narrow sense and a broad sense. Generally refers to the narrow sense of the Central Plains, that is, Henan Province in particular. The "Central Plains" in a broad sense is a vast area with Henan as the center and infiltrating into parts of neighboring provinces in Henan.

In ancient poetry, such as Lu You's "Looking north at the Central Plains like a mountain".