Large numbers of Urban Air Mobility (UAM) vehicles are expected to operate in urban airspace in the near future. However, this growth will soon exceed the capacities of current airspace and air traffic management systems and put strains on transportation infrastructure, resulting in undesirable outcomes such as traffic congestion, complex traffic situations, delays, etc. As a result, innovative UAM solutions are required to ensure safe and efficient urban transportation. In this thesis, we focus on strategic planning in unmanned aircraft system traffic management, including airspace organization and management and traffic flow management. Specifically, we develop approaches for UAM route network design and air traffic assignment. The struct...