Definition
On an instrument approach procedure (IAP) chart plan view, a circle drawn around the airport reference point that defines the scale within which features are shown to scale. Inside the circle, terrain, navaids, fixes, and other features are depicted in their correct geographic position relative to one another. Outside the circle, items may be shown out of scale to fit them on the chart, so distances and bearings between objects beyond the circle should not be measured directly from the chart.
Plain English
It is a circle on an approach chart that tells you where the chart is drawn to scale. Anything inside the circle is shown in its true position. Anything outside the circle may have been shifted to make it fit, so do not trust distances measured outside it.
Context Anchor
Seen on navigation charts, weather displays, and plotting tools when a pilot needs to judge distance from an airport, station, or other known location.
Why Pilots Care
Allows quick visual assessment of reach or position without repeated measurements, supporting fuel planning and situational awareness.
Analogy
It is like drawing a circle around your home on a map to show everything that is, for example, 10 miles away from it.
Grounding Statement
Every point on the circle is the same distance from the point at the center.
Intuition Check
Do not read the circle as a flight path or an airspace boundary by itself. In this context, it is normally a measuring aid that shows equal distance from the center point.
Example Sentence 1
The instructor pointed out that the off-airport VOR was depicted outside the reference circle, so its position on the chart was not to scale.
Example Sentence 2
Using the distance circle on the chart, she confirmed the airport was within gliding distance after the engine failure.