Definition

Noun: An isogonic line is an imaginary line drawn on a map or chart that connects all points on the Earth's surface having the same magnetic declination at a given time. Magnetic declination is the angle between magnetic north (the direction a compass needle points) and true north (geographic north).

Usage

The term is used primarily in the fields of cartography, navigation, and geophysics to describe lines of equal magnetic variation on maps, especially nautical or aeronautical charts. - The navigator plotted the course, carefully noting where it crossed several isogonic lines on the chart. - On this map, the isogonic line marked '0°' indicates the agonic line, where magnetic north and true north align.

Advanced Usage

• Isogonic Chart: A map that displays a series of isogonic lines, showing how magnetic declination varies across a region.
  • Pilots study isogonic charts to correct for magnetic variation during long flights.
• The line of zero declination is specifically called the agonic line.

Variants and Related Words

• Isogonic (Adjective): Pertaining to or denoting equal angles, especially magnetic declination.
  • The isogonic pattern on the map shows increasing declination to the east.
• Agonic Line (Noun): A specific type of isogonic line where the magnetic declination is zero.
• Isogonal Line: A synonym for isogonic line.
• Magnetic Declination (Noun): The core concept measured by isogonic lines.

Synonyms

• Isogonal line
• Line of equal magnetic declination

Related Terms and Concepts

• Magnetic Variation: Another term for magnetic declination.
• Compass Rose: A diagram on a map that shows both true north and magnetic north, often referencing local declination.
• Magnetic Pole: Either of the two points on the Earth's surface where the magnetic field is vertical; their location affects the pattern of isogonic lines.

Noun

1. an imaginary line connecting points on the Earth's surface where the magnetic declination is the same