Reference circle (also, distance circle)

Reference Circle: a circular representation found in the plan view of an Instrument Approach Procedure (IAP) chart that commonly has a radius of up to 10 nautical miles. This circle denotes the area in the chart where the elements are drawn to scale. In aviation, the use of reference circles is an essential part of procedural mapping as it allows pilots to accurately measure distances and identify the location of significant landmarks. The reference circle also helps pilots to determine the required altitude and speed in that section of the chart. These circles are prevalent in approach charts, where pilots need to know their position in relation to the airport and other fixed navigational aids. The size of the reference circle can vary depending on the size of the chart and the level of detail required to navigate safely. In summary, reference circles are a vital tool for pilots and navigator to facilitate safe flying and ensure accurate navigation during instrument approaches to airports.