Which altitude is applicable to the vertical extent of the surface and shelf areas?

The altitude that pertains to the vertical extent of the surface and shelf areas is 4,000 feet above airport. This measure specifically relates to the defined airspace where operations can occur and is a standard reference for understanding airspace classifications and regulations.

Choosing 4,000 feet above airport makes sense within the context of air traffic management and safety operations, as it establishes clear boundaries for aircraft operating in and around airports, ensuring that commands and procedures are effectively communicated to maintain orderly traffic flow. This altitude helps to segment airspace into manageable sections that support both visual flight rules (VFR) and instrument flight rules (IFR).

In practice, the other altitudes provided do not align with the operational norms or regulatory frameworks regarding the definition of surface and shelf areas, making those options less relevant in this context.