With increase in urban surface level traffic congestion, development of urban air mobility is attracting a lot of attention from researchers. Urban Air Mobility requires rules and regulations in a traffic scenario so as to deployUnmannedAerialVehicles (UAV) in urban areas. Geo-fencing is a critical component of the UAV system as it designates the strict boundaries of the lanes and sub-lanes for safety and smooth flow of UAV traffic. In this work, a novel approach for representation of geofencing using Signed Distance Functions (SDF) is presented. A geofence repulsion strategy, so that UAV does not collide with various proposed geofencing layers, and violation check using the trajectory planning strategy are proposed to ensure smooth flow of drones in the airspace. These methods are developed for CORRIDRONE, an architecture for authorizing drones in the controlled airspace, but are general enough to be used in other air mobility systems too.