Land Expansion Under Population Decline: Testing SDG Indicator 11.3.1 in Yunlin and Chiayi Prefectures, Taiwan

SDG Indicator 11.3.1, defined as the ratio of land consumption rate (LCR) to population growth rate (PGR), is widely used to assess the efficiency of urban land use. However, its applicability becomes increasingly uncertain in regions characterized by population decline, dispersed settlement structures, and mixed urban–rural land systems. This study examines the applicability and interpretive limitations of SDG Indicator 11.3.1 in Yunlin and Chiayi, two non-metropolitan agricultural prefectures in Taiwan, over 2010–2025. Using county-level population data, GHSL-based built-up area estimates, and supplementary land-use and household statistics, it calculates LCR, PGR, and LCRPGR. The results are then interpreted with supplementary indicators, including per capita built-up area (PBUA), absolute built-up area change (∆Urb), and population density within built-up areas (DBU). The results show that both prefectures experienced continued built-up expansion despite population decline, resulting in negative LCRPGR values at the prefecture level and predominantly negative values at the county level. When interpreted together with rising PBUA and declining DBU, these results indicate a process of land dilution associated with diseconomies of density and shrinkage-related sprawl, rather than compact or efficient spatial adjustment. The findings suggest that negative LCRPGR values in shrinking regions should not be interpreted as evidence of efficient land use. Instead, SDG Indicator 11.3.1 should be treated as a diagnostic starting point whose interpretation requires supplementary indicators and territorial context. By focusing on non-metropolitan agricultural prefectures, this study extends the discussion of SDG Indicator 11.3.1 beyond rapidly growing metropolitan areas and demonstrates the need for a more context-sensitive framework for evaluating land-use efficiency in low-growth and shrinking regions.