The Art Nouveau Path: Requirements Engineering and Traceability for City-Scale In-the-Wild Mobile Augmented Reality Learning Services

City-scale augmented reality (AR) learning paths are outdoor, multi-stop educational routes delivered through mobile devices in public space. This paper examines the Art Nouveau Path, a mobile AR game (MARG) route in Aveiro, Portugal, as a deployable learning service. The focus is on implementation requirements and traceability rather than learning outcomes. The analysis combined profiling of eight points of interest (POIs) and 36 tasks, group-session logs from 118 sessions, and teacher-facing evidence from a validation workshop (T1-VAL, N = 30) and on-site observation (T2-OBS, N = 24). Open-text responses were segmented into meaning units and coded with an eight-determinant taxonomy, with good intercoder reliability (Krippendorff’s alpha = 0.83). Logs and the post-path questionnaire (S2-POST, N = 439) were used only to describe enactment feasibility and data integrity. The strongest determinants concerned onboarding and legibility, marker robustness and recovery, and curriculum alignment, together with safety and fallback needs. These signals were translated into 18 testable requirements linked to six transfer artefacts for enactment, maintenance, incident handling, and fallback. Overall, the study provides an implementation-oriented specification to support auditability, replication, and transfer in city-scale AR learning services.