Analysis of urban expansion and driving forces based on Landsat imagery and nighttime light data from 2001 to 2024: a case of Pyongyang, Democratic People's Republic of Korea

Abstract

This study investigates urban expansion in Pyongyang, Democratic People's Republic of Korea (DPRK), using Landsat imagery data spanning from 2001 to 2024. The objective is to analyze the dynamics and driving factors behind Pyongyang's urban expansion. A framework based on random forest classification with feature optimization is proposed, which integrates multi-source remote sensing data. By fusing Landsat image spectral bands with nine feature indices (NDBI, IBI, NDVI, etc.), a classification accuracy of 93.2% is achieved, significantly surpassing traditional methods. The results reveal that Pyongyang's urban expansion follows a "policy-driven" pattern, with a substantial acceleration in building land expansion from 2019-2024, reaching 14 km²/year. This acceleration aligns closely with DPRK's housing policies. The study also finds a high correlation (R² = 0.98) between total nighttime light intensity(TNL) and urban expansion, indirectly indicating the influence of economic development on urbanization. Furthermore, the mechanism of "grassland priority occupation" during urban expansion is identified, providing insights into land conversion laws in closed cities in East Asia. This research contributes to a deeper understanding of urban expansion dynamics in Pyongyang and establishes a methodological paradigm for similar studies in other areas where economic statistics are unavailable.