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Isogonic lines on aeronautical charts

Remote Pilot (Part 107) practice question 21 of 22 on Operations / Airport Operations. ACS element UA.V.B.K6a · difficulty: recall. Want to answer it in a timed quiz? Use the Remote Pilot (Part 107) practice mode.

Question bank updated 2026-09-22

QUESTIONOn aeronautical charts, the broken magenta lines that connect points of equal magnetic variation are called

  1. Aagonic lines.
  2. Bmagnetic meridians.
  3. Cisogonic lines.
Show the answer and explanation

Correct answer: C. isogonic lines.

  • A — incorrect An agonic line is the line connecting points at which there is no variation between true north and magnetic north, not the general lines of equal variation.
  • B — incorrect Magnetic meridians show the direction indicated by a compass needle; the charted broken magenta lines of equal variation carry a different name.
  • C — correct Most aeronautical charts show the amount and direction of variation as broken magenta lines called isogonic lines, which connect points of equal magnetic variation.

BACKGROUND

Variation is the angle between true north (TN) and magnetic north (MN), expressed as east variation or west variation depending on whether magnetic north lies to the east or west of true north. Because the Earth is not uniformly magnetized, the compass needle usually points in the general direction of the magnetic pole but may vary in certain localities by many degrees. The exact amount of variation at thousands of selected locations in the United States has been carefully determined, and the amount and direction are shown on most aeronautical charts as broken magenta lines called isogonic lines. The line connecting points at which there is no variation between true north and magnetic north is the agonic line. Minor bends and turns in isogonic and agonic lines are caused by unusual geological conditions affecting magnetic forces in those areas.

STUDY TIP

Fix the pair in your memory by the prefix: iso- means equal, so isogonic lines join points of equal variation, while a- means without, so the agonic line is the one with no variation. Remember that both are drawn as broken magenta lines across the face of the chart, and that the amounts change slightly over time.

KEY POINTS

  • Variation is the angle between true north and magnetic north, labeled east or west.
  • Isogonic lines are the broken magenta chart lines joining points of equal magnetic variation.
  • The agonic line connects points where variation between true north and magnetic north is zero.

SOURCES

  • Remote Pilot Study Guide ch11 "Variation"
  • remote_pilot_study_guide.txt, Chapter 11: Airport Operations
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SkyDrill is not affiliated with the FAA. This is an original practice item based on 14 CFR part 107, 14 CFR part 89, and the FAA Remote Pilot – Small UAS Study Guide (FAA-G-8082-22). Regulations and handbooks are revised; confirm details against the current edition.