Fig. 4: Schematic diagram of the theoretical proposition of urban expansion.

The image on the upper left side of figure illustrates the relationship between the current boundary, inertia boundary, and inertia space, corresponding to the first theoretical proposition. The image on the lower left side of figure illustrates the ideal, moderate and limit boundaries defined based on the principle of price equilibrium, corresponding to the second theoretical proposition. The picture on the right side of figure illustrates the regulation spaces for urban expansion, corresponding to the third theoretical proposition.