The spatial palimpsest of a mountainous frontier: Migration, vertical stratification, and the evolution of Shiping's traditional settlements

Yunnan's traditional settlements, situated at the crossroads between inland China and mainland Southeast Asia, record long-term interactions among population mobility, institutions, and landscapes. However, how these interactions materially inscribed the built environment over time remains unclear. Focusing on Shiping County around Yilong Lake, this study examines settlement evolution through the lenses of mobility, the middle ground, and the material palimpsest. To achieve this, a spatial database of 1107 pre-1949 settlements and 195 heritage sites was compiled from gazetteers, historical maps, remote sensing, and surveys. By integrating kernel density analysis, statistics, and Geographical Detector models with historical interpretation, the study examines how successive waves of migration reshaped settlement patterns, institutional landscapes, and architectural forms. Results show three major phases—indigenous ethnicisation, imperial sinicisation, and modern commercial mobility—accumulated rather than replaced each other, forming a non-uniform material palimpsest shaped by vertical ecological gradients. A hybrid middle ground emerged from migration-ecology interactions, creating a spatial rewriting gradient: a thick accumulation of indigenous, Confucian, and Sino-Western forms in the lakeshore core, and a thinner, continuous indigenous baseline in the uplands. By conceptualising frontier settlements as a vertically stratified material palimpsest, this study provides a framework for interpreting layered landscapes in multi-ethnic mountainous regions.