Which of the following types of airspace is not charted due to its nature?

Controlled Firing Areas (CFAs) are not charted on aviation maps because they are designed for temporary activities where the hazardous operations occur at specific times and altitudes, which means that when the activities cease, the airspace is immediately safe for aircraft to navigate through. Because of this unique nature, CFAs do not require pilots to be restricted from the airspace; rather, they are expected to remain vigilant and aware of temporary closures.

In contrast, prohibited areas, military operations areas, and warning areas are established to provide permanent and visible restrictions or hazards to flying activity, thus necessitating charting. Prohibited areas denote regions where flight is not allowed due to security or safety reasons. Military operations areas highlight zones where military training or operations are taking place, alerting pilots to potential hazards. Warning areas are similar to military operations areas but extend over international waters and may pose risks to non-military aircraft. The key difference that makes controlled firing areas unique is their temporary and non-permanent nature, emphasizing safety without requiring charting.