From resource depletion to smart shrinkage: The infrastructure logic behind thirty years of urban expansion in Panjin City

1. The Underlying Logic of Urban Infrastructure from Changes in Built-up Areas

Urban built-up area expansion has never been merely the outward movement of geographical boundaries; it is a comprehensive reflection of infrastructure investment, land use efficiency, and regional economic vitality. A recent study published in Scientific Reports used deep learning models and a combined time-spectral-texture optimization method to conduct high-precision identification of urban expansion in Panjin, Liaoning Province, from 1990 to 2020, revealing the spatial evolution trajectory of this resource-based city during its transformation. Data show that the built-up area of Panjin increased from 312.75 square kilometers to 489.49 square kilometers, with an average annual expansion of 5.89 square kilometers and a growth rate of 56.51%. But what deserves more attention is the shift in expansion patterns—from early leapfrog and edge expansion to infill development after 2016.

This shift in pattern is not accidental. For Panjin, which built its fortunes on oil and natural gas, the restructuring of urban space after resource depletion is essentially a passive switch in infrastructure from incremental expansion to stock optimization. Globally, similar urban transformations have been observed in Germany's Ruhr region, Alberta, Canada, and elsewhere, but Panjin offers a unique sample in the Asian context: how to achieve the revaluation of land value through infrastructure reallocation, between industrial land left over from the planned economy and the demands of market-oriented development.

2. Spatial Sprawl of Resource-Based Cities and the Burden on Infrastructure

From 1990 to 2016, Panjin's expansion was dominated by leapfrog and edge extension, a common development model for resource-based cities. The scattered distribution of oil fields and the independent operation of mining areas caused urban functional zones to be fragmented from one another. Infrastructure such as roads, pipeline networks, and power supply had to extend linearly, with service efficiency per unit area far lower than that of compact cities. This sprawl model was sustainable during the resource dividend period, but as oil and gas production declined, the gap between infrastructure maintenance costs and tax revenue gradually widened.

The spatial compactness indicators in the study show that the agglomeration of impervious surfaces (i.e., hard surfaces such as buildings and roads) has been continuously declining, implying that the urban form is becoming looser. This loose form directly raises the marginal costs of municipal infrastructure: longer water supply pipeline networks, lower efficiency of public transportation routes, and greater power transmission losses. For Panjin, which is seeking economic transformation, such an inefficient spatial structure has become an obstacle to attracting new industries—high-tech industrial parks require highly concentrated supporting infrastructure, not scattered industrial enclaves.

3. The Shift After 2016: Smart Shrinkage or Urban Repair?After 2016, Panjin's expansion model shifted to infill development, which is the most policy-relevant finding of the study. Infill expansion means that the city no longer sprawls outward, but instead uses internal vacant land, redevelopment of old industrial zones, and reuse of inefficient land to meet new demand. This shift is highly consistent with the international concept of "smart shrinkage," in which resource-based cities, when facing declines in population and industrial scale, proactively adjust their spatial structure, concentrate infrastructure investment in key areas, and avoid inefficient expansion of public service costs.

From an infrastructure perspective, infill development significantly improves the utilization rate of existing capital stock. For example, upgrading roads and drainage systems within the existing built-up area saves substantial upfront capital expenditure compared to building from scratch in new districts. At the same time, greater compactness facilitates the introduction of modern infrastructure solutions such as distributed energy systems, smart grids, and district heating. Research shows that after 2016, Panjin's urban spatial compactness rebounded, creating the physical conditions for intensive infrastructure upgrading.

IV. Remote Sensing Technology: A New Analytical Tool for Infrastructure Planning

The methodology of this study itself represents a frontier trend in infrastructure planning. Traditional urban expansion monitoring relies on statistical yearbooks and field surveys, which lack timeliness and struggle to capture fine-grained spatial changes. In contrast, the deep learning and combined time-spectral-texture optimization method used in this study achieved a trajectory classification accuracy of 93.10% and an expansion timing identification accuracy of 84.24%. This technical capability is crucial for infrastructure investment decisions—governments and capital providers need to clearly identify the true boundaries of urban growth in order to avoid over-investing in roads and pipe networks in shrinking areas, thereby directing resources to regions with genuine growth potential.

Globally, the integration of remote sensing technology and infrastructure financing is accelerating. Development institutions such as the World Bank have begun using satellite data to assess the actual economic returns of urban infrastructure projects, while private capital is also using geospatial data to screen PPP projects. The Panjin case demonstrates that Chinese cities are fully capable of using advanced remote sensing technology for refined infrastructure planning, providing a more scientific basis for public investment under budget constraints.

V. Rethinking Infrastructure in the Context of Northeast China Revitalization

The Northeast China region, where Panjin is located, has long faced the dual pressures of slowing economic growth and population outflow. In this context, infrastructure investment often falls into a dilemma: continuing large-scale new construction may lead to debt accumulation and idle assets, while stopping investment may accelerate regional decline. The evolution of Panjin offers a middle path—through spatial restructuring and infill development, infrastructure investment can be more precisely matched to actual demand.From a regional development perspective, Panjin's case offers reference value for the layout of ports, energy pipelines, and transportation corridors along the coast of the Bohai Bay. As a core city of the Liaohe Delta, Panjin's port and petrochemical infrastructure still occupy a nodal position in the regional logistics network. In the future, the focus of its infrastructure upgrade is not to pursue scale expansion, but to improve the efficiency of connections with surrounding urban clusters, and to enhance competitiveness through digital transformation and intelligent upgrading of existing facilities.

VI. Long-Term Trends: From Physical Expansion to Systemic Optimization

Reviewing Panjin's urban expansion over the past three decades, its trajectory reflects the structural transformation commonly faced by China's resource-based cities. The extensive development of the 1990s, the land-finance-driven expansion of the 2000s, and the compact transformation after 2016—each step corresponds to adjustments in national infrastructure strategy. Now, as the "15th Five-Year Plan" approaches, China's infrastructure logic has clearly shifted from "whether it exists" to "whether it is good." For Panjin, this means no longer pursuing an increase in built-up area, but using more scientific methods to monitor and manage existing space.

The quantitative method provided by this study offers a replicable analytical framework for other resource-based cities—from Fuxin and Daqing in China to Houston and Aberdeen abroad. In an era when global climate infrastructure and ESG investment are receiving increasing attention, identifying the spatiotemporal patterns of urban expansion is not only an academic topic, but also a core capability in infrastructure asset management. A city is not a static engineering object, but a dynamically evolving capital system. Understanding Panjin is understanding the survival and transformation path of resource-based cities in the context of globalization.