This study analyzed urban expansion in Riyadh, London, and Seoul from 2014 to 2024 using Landsat 8 and 9 surface reflectance imagery. Four spectral indices—NDVI (Normalized Difference Vegetation Index), NDBI (Normalized Difference Built-up Index), BUI (Built-up Index), and IBI (Index-Based Built-up Index)—were applied within Google Earth Engine (GEE) to classify built-up and non-built-up areas. Annual threshold-based classification was performed, and the resulting maps were visualized using collage tables and time-series charts to track gain, loss, and overall trends. Riyadh exhibited rapid horizontal growth, with extensive built-up expansion aligned with national development plans. In contrast, London’s urban change was minimal, largely constrained by planning policies and focused on densification. Seoul revealed a dual trend of peripheral expansion and inner-city redevelopment, influenced by population demands and infrastructure projects. The results highlight significant variation in urban growth dynamics across the three cities and emphasize the need for context-specific remote sensing thresholds. Despite challenges such as vegetation interference and threshold sensitivity, the multi-index approach provides a robust and repeatable methodology for long-term urban change monitoring. The study offers actionable insights for urban planners and policymakers seeking to manage sustainable development amid growing urban pressures.