Abstract: Digital twin technology is the foundation for intelligent spatial planning. Unlike traditional engineering twins, urban digital twins, due to the dynamic and complex social factors in their objects, have lacked sufficient mapping accuracy regarding population baselines. This has made it difficult for current digital twin technology to provide accurate population information to support urban planning decisions. This paper reviews the development of urban digital twins and their technical challenges, summarizes the current mainstream methods of population mapping and their issues, and, based on the logic of “real space, real population, real demand,” proposes an innovative technological framework for the precise mapping of urban population baselines. This framework integrates a wide range of data sources, primarily government data, to build a digital platform for population baseline information that caters to governmental service needs. This technology helps achieve high granularity in urban population analysis, refined community public service provision, and high-quality territorial spatial planning.