In what scenario are the heights of airspace represented as AGL on a sectional chart?

Heights of airspace are represented as Above Ground Level (AGL) on a sectional chart when the number is shown in parentheses. This notation indicates that the altitude is measured from the terrain level beneath the airspace instead of the standard sea level. This representation is critical for pilots to understand their altitude in relation to the ground, particularly in areas with varying terrain where altitude above sea level may not provide an accurate picture of their actual clearance from the ground.

There are specific scenarios where heights are not represented as AGL. For instance, bold text typically represents the height above mean sea level (MSL), and while numbers exceeding 10,000 feet may be indicated, they are generally presented as MSL. Similarly, a NOTAM (Notice to Airmen) may provide information on temporary airspace changes, but does not alter the standard representation on sectional charts unless explicitly noted.