The ever-increasing physical and demographic complexity of metropolises has shifted the "smart city" paradigm moving away from static, data-driven automation toward dynamic, citizen-centric, and resilient structures. In this context, achieving real-time spatial intelligence and three-dimensional monitoring of dense urban environments necessitates moving beyond reliance on fixed, ground-based sensors. Adopting a comprehensive, interdisciplinary approach, this study presents a framework centered on drone technology within the smart city ecosystem, while thoroughly analyzing drone functionalities, enabling technologies, and governance challenges. Integrating drones into urban management requires the definition of a "low-altitude urban airspace" a domain where drones function as intelligent, mobile nodes within the Internet of Things and as key agents in real-time Geographic Information Systems (GIS). An analysis of operational applications reveals that the use of drones has transformed critical sectors—such as intelligent transportation systems, crisis management, medical emergencies, urban environmental monitoring, infrastructure inspection, public safety, 3D mapping, and the continuous updating of urban digital twins—while significantly reducing emergency response times. From an infrastructural perspective, the realization of these functions relies on the synergy between various enabling technologies, including edge artificial intelligence, advanced 5G/6G communication networks, unmanned air traffic management systems, service-oriented drone architectures, and blockchain-based cybersecurity protocols. Nevertheless, research findings indicate that the sustainable deployment of this technology faces profound structural, social, and technical challenges. These include citizens' concerns regarding privacy violations, noise pollution, and safety risks—such as the potential for crashes—as well as the gap between technological advancement and regulatory shortcomings concerning flights conducted beyond the operator's direct line of sight. Ultimately, transitioning from reactive management to proactive urban governance hinges on striking a balance between economic productivity and the protection of citizens' rights; this provides a comprehensive framework for urban planners and administrators to safely integrate drones into the smart cities of the future.