This paper proposes a spectrally efficient aviation strategy for unmanned aerial vehicle (UAV)-mounted transmitters (Txs) operating in a service area with heterogeneous user density. We discover that two distinct tradeoffs contribute to the network throughput: A speed-dependent tradeoff between inter-carrier interference and crowd chasing; and an altitude-dependent tradeoff between the shadowing possibility and source proximity. It is then analytically demonstrated that optimal throughput and reliability can be achieved by balancing the physical movement of UAV Tx. In concern of economical battery use, the velocity vector is optimized to obtain maximum net throughput during the UAV's flight, and computer simulations verify the feasibility of the proposed flight strategy.