The rapid advancement of Extended Reality (XR) technologies has introduced new possibilities for designing and experiencing urban spaces through virtual augmentation. However, creating precise and persistent virtual experiences in urban environments remains challenging, particularly in terms of accurate spatial registration and content placement. This work addresses these challenges through a Research through Design approach, presenting a mixed-reality application that augments the city of Tampere, Finland. Our implementation introduces three key technical contributions: First, we propose an angular accuracy measurement approach for assessing XR content placement, providing more meaningful evaluation of registration quality across varying scales and distances. Second, we present a dual-system framework combining detailed spatial mapping through the Immersal SDK with extended coverage via Google’s Geospatial API, enabling persistent content placement across diverse urban contexts. Third, we demonstrate an innovative solution for extending AR glasses support through mobile device processing, enhancing device compatibility while maintaining precise spatial registration. Through implementations in three distinct urban settings - a park, pedestrian bridge, and landmark plaza - we derive spatial design guidelines emphasizing environmental harmony, cultural relevance, spatial narrative, and navigation coherence. The effectiveness of our approach is validated through successful stakeholder engagement and international recognition. Our findings contribute to the growing understanding of how to achieve both technical precision and contextual appropriateness in urban-scale XR implementations.