Define 'visual flight rules' (VFR) as it pertains to urban aviation.

Visual flight rules (VFR) are primarily concerned with how pilots navigate and operate their aircraft in conditions that allow for visual reference to the ground and horizon. When conditions are generally clear, pilots flying under VFR are able to see and avoid obstacles, other aircraft, and navigate more freely based on visual cues. This is essential in urban aviation, where the landscape can be complex and congested with buildings and other structures.

Operating under VFR mandates that pilots maintain specific visibility and distance from clouds, ensuring they have the necessary visual references to maintain safety while flying. In urban environments, where there may be a higher density of traffic and obstacles, VFR allows pilots to manage their flight paths more intuitively and responsively.

This understanding is critical, particularly in urban aviation, because it emphasizes the importance of visibility and visual navigation in safely operating aircraft in congested airspaces. The other options do not align with the core definition of VFR, which is specifically about flying in clear weather conditions wherein visual navigation is possible.