Spatiotemporal Variations of Urban Expansion and its Relation with Geomorphological Complexity: a Case Study of the Yogyakarta Urban Region, Indonesia

Urban growth in Indonesia is accelerating, particularly in areas with complex geomorphological features. This study examines the spatiotemporal variations of built-up area expansion in the Yogyakarta Urban Region (YUR), a rapidly urbanizing area characterized by diverse landforms and significant development pressures. Using Landsat satellite imagery (2001–2022), the study employed the Landscape Expansion Index (LEI) to classify urban expansion types and the Topographic Position Index (TPI) to analyze geomorphological characteristics. The findings reveal that edge-expansion dominated upper slopes, contributing 69%, 75%, and 79% of built-up area growth in 2001–2008, 2008–2015, and 2015–2022, respectively. Simultaneously, the outlying expansion type has steadily increased, particularly in U-shaped valleys, which grew significantly from 51.35 ha (2001–2008) to 109.28 ha (2008–2015) and 219.14 ha (2015–2022), highlighting an escalating risk of urban sprawl. These findings highlight the need for targeted urban planning policies to monitor and control growth patterns in geomorphologically sensitive areas, reducing sprawl and promoting sustainable development.