Question 257Navigation General

The correct answer is D) points of equal variation. Isogonic lines on a nautical chart indicate points of equal magnetic variation, which is the angle between true north and magnetic north at a given location. These lines allow the navigator to determine the magnetic variation for a specific area, which is necessary for converting between true and magnetic bearings and courses. The other answer choices are incorrect because they do not accurately describe what isogonic lines represent on a chart. Magnetic latitude (A) and magnetic dip (B) are different concepts not directly related to isogonic lines. Points of zero variation (C) are a specific type of isogonic line, but the question asks about what isogonic lines in general indicate.