[ahy-sog-uh-nl] /aɪˈsɒg ə nl/
noun 1. an imaginary line, or one drawn on a map, connecting all points of equal magnetic declination.
[ahy-suh-gon-ik] /ˌaɪ səˈgɒn ɪk/ adjective 1. having or pertaining to equal angles. 2. noting or pertaining to an . noun 3. . /ˌaɪsəʊˈɡɒnɪk/ adjective 1. (maths) having, making, or involving equal angles noun 2. (physics) Also called isogonic line, isogonal line, isogone. an imaginary line connecting points on the earth’s surface having equal magnetic declination
isograd (ī’sə-grād’) A line on a map connecting points on the Earth where metamorphism of rocks occurred under the same pressure and temperature conditions. These lines are established on the basis of the distribution of index minerals and are useful in reconstructing the tectonic history of a given region.
[ahy-suh-grey-dee-uh nt] /ˌaɪ səˈgreɪ di ənt/ noun, Meteorology. 1. a line on a weather map or chart connecting points having the same horizontal of a meteorological quantity, as temperature, pressure, or the like.