Recently, the Zhengzhou Metropolitan Area was recognized as a national-level metropolitan area. The "Zhengzhou Metropolitan Area Development Plan" is the tenth such plan approved by the National Development and Reform Commission. In a sense, the Zhengzhou Metropolitan Area has evolved through understanding, adjustments, and optimization from the spatial structure of the Central Plains Urban Cluster.

The Central Plains Urban Cluster is a cross-provincial urban agglomeration encompassing 30 cities across Henan, Hebei, Shanxi, Shandong, and Anhui provinces. In December 2016, the State Council approved the "Central Plains Urban Cluster Development Plan." This plan included a "1+4" metropolitan area concept, centering on Zhengzhou and connecting with Kaifeng, Xuchang, Xinxiang, and Jiaozuo to form a preliminary concept for the Zhengzhou Metropolitan Area. Based on the original intention of the metropolitan area and drawing on previous plans, the newly released "Zhengzhou Metropolitan Area Development Plan" adjusts its spatial scope to a "1+1+2" model, including Zhengzhou City, Zhengzhou Airport Economic Zone, Kaifeng City, and Xuchang City. These neighboring cities and the airport economic zone constitute the current phase of the Zhengzhou Metropolitan Area, with the integration of Zhengzhou and Kaifeng as its core. The Zhengzhou Metropolitan Area is committed to interactive and coordinated development with other neighboring and surrounding cities.

In February 2019, the National Development and Reform Commission issued China's first document on metropolitan area planning and construction, "Guidelines on Fostering and Developing Modern Metropolitan Areas" ("the Guidelines"). The Guidelines define urban clusters and metropolitan areas and explain their relationship. According to the Guidelines, "An urban cluster is a new type of urbanization and an important platform supporting national economic growth, regional coordinated development, and international competition and cooperation. A metropolitan area is an urbanized spatial form within an urban cluster centered around mega-cities or large cities with strong radiation and driving functions, and typically spans a one-hour commuting circle."

Urban clusters and metropolitan areas are both inevitable products of urbanization in large countries and spatial forms of urban and regional clusters, but they have several differences.

Firstly, the difference in spatial scope. A single urban cluster generally includes two or more metropolitan areas. In the central area of the Yangtze River Delta, there are three urban clusters planned, each with two metropolitan areas. In the Chengdu-Chongqing economic circle (urban cluster), there are the Chengdu and Chongqing metropolitan areas. In the Central Plains Urban Cluster, although the next metropolitan area development plan is yet to come, it is believed that more will emerge over time.

Secondly, the difference in adjacency. The concept of "job-housing balance" evolves from the city (central urban area) to the metropolitan area. It suggests that as cities develop, the central urban areas become overcrowded, leading to new towns in the suburbs primarily for residential purposes, eventually involving nearby cities in administrative divisions. To facilitate commuting and reduce travel time, rail transit (subways, light rails, and intercity railways) emerges and develops rapidly. Therefore, cities within a metropolitan area are geographically adjacent, connected by rail transit, also known as "rail-based cities." The concept of a "greater metropolitan area" essentially refers to an urban cluster, where not all cities are geographically adjacent, with only a part being contiguous.

Thirdly, the difference in economic connections. Due to spatial distance and infrastructure, there is a difference in the closeness of economic ties within urban clusters and metropolitan areas. However, this difference also manifests in the way economic ties are established. In relatively developed areas, metropolitan areas become the main form of urban clusters. From the perspective of factor flows and industrial systems, the relationships within a metropolitan area are mainly characterized by radiation, spillover, and division of labor. In China's vast territory, in world-class urban clusters like the Yangtze River Delta and the Pearl River Delta, multiple metropolitan areas exist with high economic density, and their internal economic connections are the same as those within a metropolitan area. However, in other regions, the relationships between central cities and surrounding areas within urban clusters are primarily characterized by aggregation, absorption, and transfer. As China accelerates the construction of a modern industrial system, the relationships within other urban clusters should also be elevated to the level of radiation, spillover, and division of labor. Only then can urban clusters and metropolitan areas achieve coordinated innovation, leading to the balanced development of large, medium, and small cities.

To achieve high-quality regional development, clarifying the concepts of urban clusters and metropolitan areas helps ground the development plans of urban clusters or metropolitan areas, accelerating the construction of modern industrial systems across different spatial scopes. By strengthening and complementing industrial chains and supply chains, promoting the balanced development of basic public services and social security, and continuously improving the levels of co-construction and sharing, as well as integrating and optimizing social resources across administrative divisions, the management of natural and social ecology can be improved.

In conclusion, it is essential to clarify and correctly use the concepts of urban clusters and metropolitan areas. Over the years, the terms have often been used interchangeably, leading to ambiguities in academic research and deviations in policy-making or planning. The time has come to distinguish and accurately apply these concepts.