## 5 Discussion  
The rational allocation of urban space can improve the urban land use efficiency, resulting in promoting the harmonious development of regional economy and environment. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Classification** & **Basis** & **Amount** & **Category** & **Reference** \\ \hline National standards & Urban land intensive utilization potential evaluation regulation (Trial) & 5 categories & Special function land, residential function land, industrial function land, educational function land & [106] \\  & Standard for Basic Terminology of Urban Planning & 11 categories & Residential land, industrial land, public facilities, municipal utilities, road and squares, intercity transportation land, warehouse land, specially-designated land, green space, waters, and miscellaneous & [107] \\  & Regulatory plan & 4 categories & Residential, living, and commercial areas, production areas, leisure and green areas, urban supporting functional areas & [108] \\ Urban planning & Constructive-detailed plan & 3 main categories & Production service functional area, infrastructure type functional area, special function area & [109] \\  & & & Administrative office, financial business district, commercial service area, tourism and entertainment area, scientific research industry zone, cultural education district, industrial R\&D zone \\  & & 16 categories & Transportation hub, city facility service area (water, electricity, heating and other facilities), historical sites, logistics park, residential area, green ring environmental area (rivers and lakes) & [108] \\  & Main functional area planning & 4 categories & Military facility area, civil air defense construction area & [110] \\  & Functional characteristics & 6 categories & Residential areas, industrial areas, commercial areas, public management and public service areas, green space and square areas, road and traffic facility areas & [33, 34, 45] \\ Main nature of land use & Trajectory characteristics & 4 categories & Residential areas, industrial parks and office areas, commercial and leisure areas, nighttime areas & [23, 24, 85] \\  & Image characteristics & 4 categories & Commercial office zones, urban green zones, industrial warehouse zones, residential zones & [49, 57] \\  & Functional and trajectory characteristics & 7 categories & Develop residential areas, emerging residential areas, scenic areas, commercial and entertainment areas, science/education/technology areas, and other areas to be developed & [2, 29, 90] \\  & Functional and image characteristics & 8 categories & Urban green, industrial districts, public services, shanty towns, residential districts, schools, commercial districts, hospitals & [51, 96, 97] \\  & Regional economy & 2 main categories & Economic functional areas & \\  & Regional economy & 6 categories & Non-economic functional areas, business areas, industrial areas, tourist areas residential areas, administrative areas, Capital administrative areas, commercial central areas, financial and business areas, historical preservation areas, transportation hub areas, cultural and entertainment areas, hospitals, schools and other crowded areas, public leisure areas, and residential areas & [111] \\  & Urban functions & 4 categories & Ecological conservation development areas, new urban development areas, urban function expansion areas, capital functional core areas & [112] \\  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: General classification schemes of urban functional zones. Many studies have discussed the classification, distribution, and driving factors of urban functional zones, which provides references for urban spatial structure examination, land use planning verification, and urban functional form optimization. Although there are some achievements in urban functional zones studies, limitations still existing. 1. Because of inhomogeneous data in urban areas, it is difficult to identify functional zones in some areas with poor data, which affects the accuracy of functional zone identification.