An imaginary line connecting points where the magnetic declination is zero at a given date is known as what?

The correct answer is the agonic line, which is defined as an imaginary line that connects points on the Earth's surface where the magnetic declination is zero. This means that at these points, the magnetic north aligns exactly with true north, indicating no deviation or declination between the two. Understanding the concept of the agonic line is crucial for navigators and individuals involved in search and rescue operations, as it helps in accurately determining directions without the need for correcting for magnetic declination.

In contrast, the isoclinic line relates to locations where the magnetic field's inclination is the same; the isogonal line connects points with the same magnetic declination, but not necessarily zero. Equidistant lines typically refer to geographic or mathematical concepts concerning equal spacing, not directly tied to magnetic declination. Therefore, the agonic line is specifically significant because it indicates a point of no magnetic declination, crucial for navigation accuracy.