Urban Morphological Evolution and the Spatial Restructuring of Carbon Emissions in High-Density Taipei: A 3D Historical GIS, XAI, and MGWR Analysis, 1980–2025

Compact development is often treated as a low-carbon strategy, yet high-density cities may face new carbon pressures as vertical development, agglomeration, and cross-district commuting intensify. This study examines Taipei using 27,239 100 m × 100 m grid cells and 1980–2025 data integrating Historical GIS, remote sensing, official LOD1 building models, energy statistics, and anonymized commuting origin–destination data. XGBoost, TreeSHAP, multiscale geographically weighted regression (MGWR), CASA, and network analysis served as complementary instruments. The carbon-emission compound annual growth rates of existing built-up cells were 2.994% in the historic western districts and 2.890% in the emerging eastern districts (p = 0.104); the larger long-term increase in the east (approximately 195% versus 166%) is more consistent with extensive-margin expansion. TreeSHAP identified breakpoints at 12.83 for nighttime lights, 197.67 buildings/km² for building density, and 99.61 for FAR × Nightlight. MGWR achieved an adjusted R² of 0.886 and revealed marked multiscale spatial non-stationarity. Commuting flows further indicated cross-boundary carbon-burden asymmetry. The findings recast compact-city benefits as contingent on development margins, morphological thresholds, spatial scale, and functional urban networks. As an observational reconstruction, the study supports predictive and spatial associations rather than strict causal effects.