Which term describes lines that show zero magnetic variation, aligning with true north?

• A. Agonic Lines
• B. Isogonic Lines
• C. Magnetic Meridian
• D. True Meridian

Answer: (A)

Lines with zero magnetic variation occur where the magnetic north and true north align. This is called an agonic line, because along it the declination is zero and a compass points directly toward true north without any offset.

Isogonic lines, by contrast, are lines where the magnetic variation has the same nonzero value, so the compass would deviate by that fixed angle along them. The magnetic meridian is the vertical plane containing the magnetic field direction, not about aligning with true north. The true meridian is the geographic north–south line, independent of magnetic effects.